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.”

The decision came after Ukraine’s first strike on Russian territory with U.S.-supplied long-range weapons and President Joe Biden authorized the provision of antipersonnel land mines to Ukraine to help fight off Moscows forces.

The embassy said in a security alert that it had closed “out of an abundance of caution,” and employees were “being instructed to shelter in place.” It added that U.S. citizens should take shelter if an air alert was announced.

Shutting the embassy is not an unprecedented move amid the war, which reached its 1,000th day Tuesday. The Italian and Greek embassies said they had also closed their doors after the U.S. warning. The French embassy remained open but urged its citizens to be cautious.

Later Ukraine’s Defense Intelligence Directorate said on Telegram that Russia was “conducting a massive information and psychological attack.” It added that a “fake” message containing grammatical errors was “being spread through messengers and social networks.”

The warning came after Defense Secretary Lloyd Austin said the decision to supply the landmines to Ukraine came after the Russians changed tactics on the battlefield.

Russian ground troops are leading the movement on the battlefield, rather than forces more protected in armored carriers, so Ukraine has “a need for things that can help slow down that effort on the part of the Russians,” he told reporters during a trip to Laos.

The mines “which can be rapidly deployed, are designed to blunt the advances of ground forces, and, as such, will significantly support Ukraine’s defense against Russian advances in its sovereign territory, particularly in the east, especially when used in concert with the other munitions that the United States provides Ukraine,” a U.S. official told NBC News.

The U.S. had “sought commitments from the Ukrainians on their use, to further limit the risk to civilians” and it was expected that “Ukraine would use these mines on its own territory,” the official said.

Unlike Russian mines, the official said the U.S. mines were “non-persistent” and would become inert after a preset period of time, anywhere between two to four weeks and would not detonate after their batteries ran out.

However, the International Campaign to Ban Landmines said on X it was “inconceivable” the U.S. would provide the weaponry “as the world’s largest donor to mine clearance.” Urging the Biden administration to reverse the decision, it said the “protection of civilians cannot be compromised, even in extraordinarily difficult circumstances.”

In Ukraine, more than a dozen people have been killed in an intensified wave of Russian aerial attacks, which have targeted energy infrastructure across the country and forced widespread blackouts.

And 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.

Elsewhere in Kyiv, officials said a kindergarten and several other buildings were hit.

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 countrys nuclear doctrine, lowering the threshold for his countrys 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.

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, Courtney Kube from Washington and Mithil Aggarwal from Hong Kong.

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