The US government on Wednesday said its embassy in Kyiv will remain shut on Wednesday after receiving information about a possible air attack in Ukraine.

"The U.S. Embassy in Kyiv has received specific information of a potential significant air attack on November 20.  Out of an abundance of caution, the Embassy will be closed, and Embassy employees are being instructed to shelter in place," the US government said in a statement.

The US further instructed its citizens currently present in the country to be prepared to immediately shelter in the event an air alert is announced.

The alert was issued just a day after Ukraine reportedly fired US-supplied long-range missiles at Russian territory for the first time since Washington permitted Kyiv to conduct such attacks.

As per CNN report, Russia’s Defence Ministry said Ukraine fired six ballistic missiles at a facility in Bryansk at 3:25 a.m. local time (7:25 p.m. ET) Tuesday and that ATACMS missiles had been used in the attack.

It is the first time Ukraine used the longer-range American weapons to strike targets deep inside Russia.

Ukrainian President Volodymyr Zelenskyy did not confirm striking Russia with the ATACMS missiles.

During a press conference on Tuesday, the Ukrainian President was quoted as saying by CNN: "Ukraine has long-range capabilities. Ukraine has long-range drones of its own production. We now have a long ‘Neptune’ (Ukrainian cruise missiles) and not just one. And now we have ATACMS. And we will use all of this.”

The US has not officially commented on the strikes so far.

US President Joe Biden recently authorised Ukraine long-range American missiles inside Russia.