“Out of an abundance of caution, the Embassy will be closed, and Embassy employees are being instructed to shelter in place,” a statement published on the embassy’s official website stated.

The embassy also urged Americans in Ukraine to follow the directions of Ukrainian officials and first responders in the event of an emergency and to monitor local media.

The Italian and Greek embassies in Kyiv also shut to the public for the day. The British government said that its embassy in the city remained open.

The warning comes a day after Russia’s Ministry of Defense reported that Ukraine used U.S.-made long-range Army Tactical Missile Systems (ATACMS) to strike its territory.

Russia’s Ministry of Defense said Russian forces shot down five of six missiles fired at a military facility in the Bryansk region.

Fragments from one of the missiles hit the military facility, causing a fire that was quickly extinguished and caused no casualties or damage, according to the ministry.

“According to confirmed data, U.S.-made ATACMS [Army Tactical Missile Systems] … have been used,” the defense ministry said in a statement.

The White House has not yet confirmed whether Ukraine has been authorized to use U.S. weapons against targets in Russia, however, anonymous U.S. officials who spoke to media outlets said Biden authorized Ukraine to use the missiles to strike targets in Russia.

Biden, who is set to leave office in two months, has previously been opposed to the idea of allowing U.S. missiles to be used deep inside Russia.

Moscow has repeatedly warned that such a move by the United States would be tantamount to direct involvement in the conflict and would trigger a response.

Putin Updates Nuclear Doctrine

Russian President Putin signed an updated nuclear doctrine on Nov. 19, lowering the threshold for using nuclear weapons. The updated doctrine now states that an attack on Russia by any nation using conventional missiles supplied by a nuclear power will be considered a joint attack on Russia.

Following the move, the White House said it has no plans to adjust its nuclear posture in response to Russia’s actions.

“As we said earlier this month, we were not surprised by Russia’s announcement that it would update its nuclear doctrine; Russia had been signaling its intent to update its doctrine for several weeks,” the White House National Security Council said in a statement.

Kremlin spokesman Dmitry Peskov on Nov. 18 accused the Biden administration of “adding fuel to the fire” and “provoking further escalation.”

“President Putin has already explained it very simply. Ukraine does not carry out these strikes. After all, the strikes are carried out by those countries that give permission, because the Ukrainian military does not acquire the targets and provide the maintenance,” Peskov said. “This is done by military specialists from these Western countries, and this fundamentally changes the modality of their involvement in the conflict. This is the danger and the provocative nature of this situation.”

Earlier this month, Washington accused Russia of attempting to escalate the conflict by deploying more than 10,000 soldiers from North Korea to eastern Russia.

At the time, Ukraine’s President Volodymyr Zelenskyy condemned what he called a lack of response from Western allies over the move.

The Ukrainian leader has not yet commented on the alleged use of U.S.-made long-range missiles in Russia but he said during a joint press conference, alongside Danish Prime Minister Mette Frederiksen in Kyiv earlier this week, that Ukraine has “long-range capabilities, including domestically produced drones, the Neptune (cruise missile), and now ATACMS.”

Zelenskyy added that Ukraine “will use all of these.”

Owen Evans and Reuters contributed to this report.