The United States said Wednesday that its embassy in the Ukrainian capital, Kyiv, had closed after receiving "specific information of a potential significant air attack."
"Out of an abundance of caution, the Embassy will be closed, and Embassy employees are being instructed to shelter in place," it said in a security alert, recommending U.S. citizens take shelter if an air alert is announced.
Shutting the embassy is not an unprecedented move amid the war, which reached its 1,000th day Tuesday.
The Ukrainian capital came under attack by Russian drones early Wednesday, said the head of Kyiv’s City Military Administration, Serhii Popko, adding that debris had fallen in the Dniprovskyy district.
"A fire broke out in an apartment of a multi-story residential building," he wrote in a post on Telegram, adding that information about the victims was being clarified.
More than a dozen people have been killed in an intensified wave of Russian aerial attacks, which have targeted energy infrastructure across Ukraine and forced widespread blackouts.
The renewed threat to Kyiv follows news that Ukraine carried out its first strike on Russian territory with U.S.-supplied long-range weapons, hitting a military facility in the Bryansk region with ATACMS missiles.
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The Kremlin has reacted furiously to the relaxation of U.S. restrictions on its ally, and early Tuesday Russian President Vladimir Putin formally revised his country's nuclear doctrine, lowering the threshold for his country's use of nuclear weapons.
Moscow could justify a nuclear strike if subject to an attack by a nonnuclear country that is supported by a nuclear country, according to the revised doctrine.
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A spokesperson for the embassy said the closure was unrelated to Putin's announcement, and was "related to the ongoing threats of air attacks." Staffers are working remotely, the spokesperson told NBC News.
As Russia ramps up its assault of Ukrainian skies, Kyiv has also stepped up its strikes across the border.
When asked by reporters if Putin had changed his daily routine after the U.S. policy reversal, Kremlin spokesperson Dmitry Peskov said Wednesday, "no changes there."
Overnight, Russia intercepted 44 Ukrainian drones, the Russian defense ministry said on Telegram.
Three of the drones were shot down over the Belgorod border region, the ministry said, where the Ukrainians said they struck a Russian command post.
Daryna Mayer reported from Kyiv, Ukraine and Mithil Aggarwal from Hong Kong.
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