This was CNBC's live blog tracking developments on the war in Ukraine.

Russia's Dmitry Medvedev said on Friday that the Kremlin isn't bluffing over its threats to use tactical nuclear weapons against Ukraine.

In a Google-translated post published on his official Telegram channel, Russia's former president said Moscow's use of tactical nuclear weapons can be "miscalculated" but that the Kremlin's position on the potential deployment of these weapons was not "not intimidation or nuclear bluff."

His comments come shortly after reports said U.S. President Joe Biden had quietly given permission to Ukraine to allow its forces use U.S. weapons inside Russia. The decision only applies to counter-fire purposes in the area around Ukraine's northeastern region of Kharkiv.

Russian missiles hit several locations in Ukraine's northeastern Kharkiv region overnight, killing five people and injuring at least 25, according to the regional head. Oleh Syniehubov described the evening as a "difficult night for Kharkiv."

CNBC could not independently verify developments on the ground.

China has reportedly turned down the chance to attend Ukraine's peace conference in Switzerland next month.

Beijing has declined an invitation to join the June 15-16 summit because the conditions necessary for them to participate were not met, Reuters reported, citing three unnamed sources with direct knowledge of the matter.

Pictures show destruction in Ukraine's Kharkiv region

Pictures taken Friday show destruction in Ukraine's northeastern region of Kharkiv after Russian missiles hit several locations there in the night from Thursday to Friday.

Earlier on Friday, regional head Oleh Syniehubov described the evening as a "difficult night for Kharkiv."

— Sophie Kiderlin

Ukraine to raise electricity prices by more than 60% from Saturday, lawmaker says

Ukraine's government is raising electricity prices for the public by more than 60% from Saturday, lawmaker Oleksiy Kucherenko said on Friday.

The power sector has been severely damaged by Russian bombardments during more than 27 months of war, while the government in Kyiv needs additional funds to be able to finance its large-scale repair campaign.

— Reuters

U.S.' Blinken confirms that Washington approved Ukraine using U.S. weapons inside Russia

U.S. Secretary of State Antony Blinken on Friday confirmed that the U.S. President Joe Biden approved Ukraine's usage of weapons supplied by the U.S. within Russia. This only applies to Russian targets that are attacking Ukraine's Kharkiv region.

"Over the past few weeks, Ukraine came to us and asked for the authorization to use weapons that we're providing to defend against this aggression, including against Russian forces that are massing on the Russian side of the border and then attacking into Ukraine," Blinken said at a news conference following an informal meeting of NATO foreign ministers in Prague.

"And that went right to the President, and as you've heard, he's approved use of our weapons for that purpose. Going forward, we'll continue to do what we've been doing, which is as necessary adapt and adjust," he said.

News of Biden approving the use of U.S. weapons in this way first emerged on Thursday. Biden had previously been against the use of U.S. supplied weapons by Ukraine to carry out strikes on Russian territory.

— Sophie Kiderlin

Ukraine signs security deals with Sweden, Norway, Iceland

Ukraine on Friday signed security agreements with Sweden, Norway and Iceland.

The agreements all cover additional financial and other forms of support for Ukraine, statements published on Zelenskyy's website outlined.

Ukrainian President Volodymyr Zelenskyy earlier in the day said on social media platform X that he was in Sweden for the third Ukraine-Northern Europe summit and was meeting various regional leaders.

Sweden is set to provide military assistance worth 6.5 billion euro ($7.13 billion) between 2024 and 2026, as well as air defense systems, specialized aircraft used for surveillance, artillery and other military support. Iceland will support Ukraine financially in the years to come and help procure, finance and deliver military supplies and equipment to Kyiv. Finally, Norway will also boost its monetary support and help develop Ukraine's modern combat aircraft and maritime capabilities.

The three new agreements take the total number of security deals Ukraine has with Western countries to 15. That includes arrangements with the other two Nordic countries, Denmark and Finland, which also participated at Friday's summit.

— Sophie Kiderlin

Finland, Estonia call for additional defense spending

Russian border countries Finland and Estonia on Friday called for a boost to defense spending to protect nations against aggression from their neighbor, Reuters reported.

At the Shangria-La Dialogue security summit in Singapore, Estonian Defence Minister Hanno Pevkur said that the country was advocating for the NATO coalition to increase the amount its members should spend on defence from 2% to 2.5% of their gross domestic product ahead of the NATO summit in July.

"We clearly see there are shortages and challenges for the NATO countries in order to be ready to defend our alliance and this is why we need to increase rapidly our defence spending," he said.

Meanwhile, Finnish Deputy Defense Minister Esa Pulkkinen said decisions around command and control arrangements that will be made at the NATO summer reunion would be "of crucial importance."

"We saw that Russia is capable and willing to wage a full-scale war on its neighbour," Pulkkinen said. "It became clear that no small state could cope by themselves when brutally attacked by a much bigger enemy."

— Sophie Kiderlin

G7 and three allies 'gravely concerned' by relationship between Russia and North Korea

Members of the Group of Seven, alongside Australia, New Zealand and South Korea, on Friday said they were "gravely concerned" by the relationship between Russia and North Korea.

"We are gravely concerned by the deepening DPRK [Democratic People's Republic of Korea]-Russia cooperation in flagrant violation of multiple United Nations Security Council resolutions," they said in a statement released by the Italian Ministry of Foreign Affairs.

The signatories said they stood in "resolute opposition" to the transfer of weapons from North Korea to Russia, which they said were used in the war against Ukraine.

"We call on the DPRK and Russia to cease unlawful arms transfers and urge the DPRK to take concrete steps towards abandoning all nuclear weapons, ballistic missiles and related programmes in a complete, verifiable and irreversible manner."

Also on Friday, the European Union said in a statement it had sanctioned nine North Korean individuals and entities, in connection with North Korea's military support to Russia's war in Ukraine, as well as with the Asian country's activities to raise funds for its nuclear program.

— Sophie Kiderlin

Ukraine has already tried striking Russian soil with U.S. weapons, Kremlin says

Ukraine has already attempted to strike Russian territory with weapons supplied by the U.S., Russian state media agency Ria Novosti quoted a Kremlin spokesperson as saying.

"We know that, in general, attempts are already being made to strike Russian territory with American-made weapons," Kremlin spokesperson Dmitry Peskov said, according to a Google-translation of his quotes.

This was enough for Russia and showed how much the U.S. is involved in the conflict, he added.

Ukraine's Ministry of Defense did not immediately respond to a CNBC request for comment on the matter.

Reports that U.S. President Joe Biden gave Ukraine permission to use weapons provided by the U.S. inside Russia first emerged Thursday. This however only applies to counter-fire purposes in the area around Ukraine's Kharkiv region.

— Sophie Kiderlin

Ukraine, Russia exchange 150 prisoners of war

Russia and Ukraine have exchanged 150 prisoners of war, 75 each, the Russian Ministry of Defense said in a post on Telegram on Friday.

Released Russian military personnel would be transported to Moscow for treatment and rehabilitation, the ministry said according to a Google translation of the post.

The United Arab Emirates provided mediation support during the exchange, it added.

Ukrainian President Volodymyr Zelenskyy confirmed that 75 prisoners of war had been returned to the country in a post on social media. This included members of the armed forces, national guard, border guards and civilians, he said.

"We are making every effort to find each and every one of our people. I am grateful to the team responsible for the exchanges," Zelenskyy said.

— Sophie Kiderlin

NATO chief dismisses Russian warnings of escalation after lifting of arms restrictions

NATO chief Jens Stoltenberg on Friday dismissed warnings by Russian President Vladimir Putin that allowing Kyiv to use Western weapons for strikes inside Russian territory might lead to an escalation.

Speaking on the sidelines of a NATO foreign ministers' meeting in Prague, Stoltenberg said the alliance had heard such warnings many times before.

"This is nothing new. It has (...) been the case for a long time that every time NATO allies are providing support to Ukraine, President Putin is trying to threaten us to not do that," he told reporters.

"And an escalation – well, Russia has escalated by invading another country."

Putin on Tuesday warned NATO members against allowing Ukraine to fire their weapons into Russia and raised anew a risk of nuclear war after several allies lifted restrictions imposed on the use of weapons donated to Kyiv.

— Reuters

Ukraine can use weapons supplied by Germany to defend Kharkiv region, Berlin says

Ukraine can use weapons supplied by Germany to defend itself in the Kharkiv border region, a spokesperson for the German government said Friday.

Many countries around the world are supporting Ukraine politically, economically and with weapons, and there are agreements with Ukraine that it would use those weapons in line with international law, the spokesperson said in a statement.

"Together with our closest allies and in close dialogue with the Ukrainian government, we adjust our support continuously according to the developments in the war," the statement said, according to a CNBC translation.

Russia has prepared and carried out attacks on Ukraine, and especially Kharkiv, from adjacent Russian border regions, it added.

"Together we are convinced that Ukraine has the right, according to international law, to defend itself against these attacks. To do so, it can use the supplied weapons in accordance with international legal obligations, including the weapons supplied by us."

— Sophie Kiderlin

Russia says Biden's decision on U.S.-provided weapons to Ukraine won't affect course of war

Russian lawmaker Andrey Kartapolov, who heads the lower house of parliament's Defense Committee, said on Friday that U.S. President Joe Biden's decision to allow Ukrainian forces to use U.S. weapons inside Russia will not impact the course of the war.

"It will not affect the course of the SMO [Special Military Operation] in any way," Kartapolov said, according to an NBC translation.

"They [threats] will remain as before. But threats will emerge for them. Because since they are increasing the degree of escalation, okay, we will respond. Asymmetrically, but with an impact," he added.

Kartapolov's comments were first reported by Russian state agency Sputnik.

Russia continues to characterize its full-scale invasion of Ukraine as a "special military operation" after more than two years of war.

— Sam Meredith

Russian court extends detention of Russian-U.S. journalist Kurmasheva

A Russian court on Friday extended until Aug.5 the pre-trial detention of journalist Alsu Kurmasheva who hold Russian and United States citizenships, a Reuters correspondent reported from the courtroom in the city of Kazan.

Kurmasheva is a Prague-based journalist for Radio Free Europe/Radio Liberty (RFE/RL), which is funded by the U.S. Congress and designated by Russia as a foreign agent, meaning it gets foreign funding for activity deemed to be political.

Her employer says her detention on charges of violating Russia's law on foreign agents is unjust and politically motivated.

— Reuters

Former Russian president says Moscow isn't bluffing over threats to use tactical nuclear weapons

Russia's Dmitry Medvedev on Friday said the Kremlin isn't bluffing over its threats to use tactical nuclear weapons against Ukraine, warning that its conflict with the West could escalate into what he described as "the worst possible scenario."

In a Google-translated post published on his official Telegram channel, Russia's former president said the use of tactical nuclear weapons can be "miscalculated" but that the Kremlin's position on the potential deployment of these weapons was not "not intimidation or nuclear bluff."

Medvedev, who currently serves as deputy chairman of Russia's influential Security Council, was president of Russia between 2008 and 2012.

His comments come shortly after reports said that U.S. President Joe Biden had quietly given permission to Ukraine to allow its forces use U.S. weapons inside Russia. The decision only applies to counter-fire purposes in the area around Ukraine's northeastern region of Kharkiv.

— Sam Meredith

Russia says Ukrainian forces have retreated as much as 9 km in key areas of Kharkiv

Russian Defense Minister Andrei Belousov on Friday said Ukrainian forces had retreated as much as 9 km (5.6 miles) in key areas of the northeastern Kharkiv region, Reuters reported, citing the Interfax news agency.

Belousov reportedly claimed that Russian forces had captured more than 28 settlements in Ukraine this month and taken control of a total area of 880 square kilometers (equivalent to an area slightly larger than New York City) so far this year.

CNBC could not independently verify developments on the ground.

Ukraine's Foreign Ministry was not immediately available to comment.

— Sam Meredith

EU's 14th sanctions package must target circumvention, energy exports, Zelenskyy advisor says

The European Union's upcoming 14th sanctions package against Russia must do more to choke off energy exports and clamp down on circumvention by third parties, an advisor to the office of Ukraine President Volodymyr Zelenskyy told CNBC.

Vladyslav Vlasiuk said it was also vital to tighten export controls on critical technologies used within Moscow's military equipment. However, he noted that EU states would need to work more cohesively for sanctions to stand a chance of crossing the line by the end of next month as planned.

"The most critical aspect of the 14th sanctions package is its adoption by the end of June, but some member states currently pose a challenge to this," Vlasiuk said via email Thursday.

The EU's special envoy for the implementation of sanctions, David O'Sullivan, was in Kyiv Thursday to discuss the latest sanctions package amid ongoing pushback from member states such as Hungary. Among the proposed measures is a ban on Russian liquified natural gas (LNG) exports and a crackdown on sanctions circumvention via countries including Kremlin ally Belarus.

Nataliia Shapoval, a member of the Yermak-McFaul International Working Group on Russian Sanctions, a think tank which advises on EU sanctions, said the LNG proposals were an attempt to restrict both Russia's current and future energy revenues.

"LNG is the leverage that Russia still maintains," Shapoval said over the phone.

Russia said Wednesday that such a ban would hurt the EU more than it would Russia, and that some LNG supplies were already being redirected to China and India. Shapoval noted, however, that gas supplies were much more difficult to direct without European infrastructure than, for example, oil.

She added that the EU was currently playing a "cat and mouse game" to determine which critical components were propping up Moscow's military might and should therefore be banned.

— Karen Gilchrist

Ukraine says Russian missiles hit multiple sites in Kharkiv, killing five

Russian missiles hit several locations in Ukraine's northeastern Kharkiv region overnight, killing five people, according to the head of the Kharkiv region.

Oleh Syniehubov said via Telegram that Russian rocket attacks took place at several locations, hitting residential and administrative buildings and damaging emergency vehicles.

Syniehubov said five people died in what he described as a "difficult night for Kharkiv."

CNBC could not independently verify developments on the ground.

— Sam Meredith

Two injured in Russia's Krasnodar region after Ukrainian attack on an oil depot, local officials say

A Ukrainian air strike on Friday hit an oil depot in the Krasnodar region of southern Russia, setting the facility on fire and inuring two employees, Russian officials said.

Krasnodar Governor Veniamin Kondratyev said via the Telegram messaging app that three of the depot's petroleum tanks caught fire after the attack.

CNBC could not independently verify developments on the ground.

Fedor Babenkov, the head of the Temryuk district in the Krasnodar region, said in a Google-translated post via Telegram that the fire had since been extinguished.

"As a result of the emergency, two oil depot employees were injured. Doctors recorded minor injuries on the men; their health was not in danger," Babenkov said.

— Sam Meredith

China reportedly turns down invitation to join Ukraine peace talks

China has declined an invitation to attend a Ukraine peace conference due to be held in Switzerland next month, Reuters reported Friday, citing four unnamed sources with direct knowledge of the matter.

Beijing turned down the offer to attend because the conditions necessary for them to participate were not met, Reuters said, citing three of the sources.

The Chinese Embassy in London did not immediately respond to CNBC's request for comment.

At the request of Ukrainian President Volodymyr Zelenskyy, Switzerland is set to hold peace talks on June 15 and 16. The aim of the conference is to bring heads of state together to chart a course for lasting peace in Ukraine, although the Kremlin has not been invited to attend.

— Sam Meredith

Russian missile attack sparks fire in Kyiv, Ukraine military says

A Russian missile attack early Friday sparked a fire at a non-residential building in Ukraine's capital of Kyiv, according to the head of the city's military administration.

In a post published via the Telegram messaging app, Serhiy Popko said a fire broke out in Kyiv's Holosiivskyi district as a result of falling debris. There were no injuries reported, according to preliminary information.

CNBC could not independently verify developments on the ground.

— Sam Meredith

NATO chief says 'time has come' to re-consider restrictions on weapons sent to Ukraine

NATO chief Jens Stoltenberg on Thursday said it was time for members of the military alliance to re-consider restrictions placed on weapons they send to Ukraine, Reuters reported.

Allies were sending various types of limitary support to Ukraine, and any restrictions on the support are national decisions, he said ahead of a NATO foreign ministers' meeting.

"But I think that in light of how this war has evolved ... the time has come to consider some of these restrictions, to enable the Ukrainians to really to defend themselves."

Opinions on restrictions on weapons and military supplies are split among Ukraine's allies. Some including the U.K. have said Ukraine could use weapons it supplied for strikes on Russian soil, while Italy has said weapons it supplied should only be used within Ukraine.

— Sophie Kiderlin

Sri Lanka tightens controls to stop men being duped into Ukraine fighting

Sri Lanka will tighten controls to try to stop its men being lured to Russia to fight in Ukraine with often false promises of salaries and benefits, a minister said on Thursday.

Colombo will also send a delegation to Moscow in June to bring back dozens of Sri Lankans already fighting in the front line who want to come home, some of them wounded, State Minister for Foreign Affairs Tharaka Balasuriya told reporters.

Countries across the region, including India and Nepal, have raised the alarm about their men being persuaded to travel to fight for Russia in Ukraine with offers of salaries, visas and sometimes university places.

Russia's ambassador to Sri Lanka, Levan S. Dzhagaryan, told the press conference on Thursday his embassy would cooperate with the efforts to stop Sri Lankans travelling illegally to Russia. He said his government was not involved in the recruitment offers.

Under the new controls, men will have to produce a "no-objection" document from the Sri Lankan defence ministry when they apply for a tourist visa to Russia, Tharaka Balasuriya told reporters.

— Reuters

Read CNBC’s previous live coverage here:

Italy says no to Ukraine using Western weapons to strike military targets inside Russia