kyiv, Ukraine (AP) — U.S. and other Western embassies in kyiv said they would remain closed Wednesday for security reasons, with the U.S. delegation saying it had received a warning about a potentially significant Russian air attack against the Ukrainian capital.

The precautionary measure came after Russian officials promised a response to President Joe Biden’s decision let Ukraine strike targets on Russian soil with American-made missiles – a decision that angered the Kremlin.

The US embassy said its closure and attack warning was issued against the backdrop of ongoing Russian missile and drone attacks on kyiv and that it anticipated a rapid return to regular operations.

The Italian and Greek embassies were also closed to the public for the day, but the British government said its embassy remained open.

The warwhich reached its 1,000 day milestone Tuesday, took on an increasing international dimension with the arrival of North Korean troops will help Russia on the battlefield — a development that U.S. officials say prompted Biden to policy change.

Russian President Vladimir Putin then lowered the threshold for using its nuclear arsenal, with the new doctrine announced Tuesday enable a possible nuclear response by Moscow, even to a conventional attack against Russia by any nation backed by a nuclear power.

This could potentially include U.S.-backed Ukrainian attacks.

Western leaders dismissed the Russian move as an attempt to dissuade Ukraine’s allies from providing further support to kyiv, but the escalation tensions weigh on the stock markets after Ukraine used US-made ATACMS longer-range missiles for the first time to strike a target in Russia.

Western and Ukrainian officials say Russia is stockpiling powerful long-range missiles, possibly with the aim of destroying Ukraine’s power grid as winter approaches.

Military analysts say the U.S. decision on the range over which U.S.-made missiles can be used is unlikely to be a game-changer in the war, but could help weaken the Russian war effort, according to the Institute for the study of war. War, a Washington think tank.

“Long-range Ukrainian strikes against military installations in Russia’s rear are crucial to degrading Russian military capabilities across the theater,” he said.

Meanwhile, North Korea recently supplied additional artillery systems to Russia, according to South Korea. He said North Korean soldiers have been assigned to Russian maritime and airborne force units and some of them have already started fighting alongside Russians on the front lines.

Ukraine struck a factory in Russia’s Belgorod region that makes cargo drones for the armed forces in an overnight attack, according to Andrii Kovalenko, head of the counter-disinformation branch of the Ukrainian Security Council.

He also claimed that Ukraine had struck an arsenal in Russia’s Novgorod region near the town of Kotovo, located about 680 kilometers (420 miles) behind the Ukrainian border. The arsenal stored artillery ammunition and various types of missiles, he said.

It has not been possible to independently verify these claims.

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