The U.S. Embassy in Kyiv, Ukraine, issued a warning after receiving “specific information of a potential significant air attack” allegedly taking place on Wednesday.

The embassy in Ukraine’s capital is temporarily closed following the alert and employees are being asked to prepare to shelter in place.

“The U.S. Embassy recommends U.S. citizens be prepared to immediately shelter in the event an air alert is announced,” the statement said.

PUTIN SIGNS REVISED DOCTRINE LOWERING THRESHOLD FOR NUCLEAR RESPONSE IF RUSSIA IS ATTACKED

Employees have been asked to take the following actions:

• Monitor local media for updates
• Identify shelter locations in advance of any air alert
• Immediately take shelter if an air alert is announced
• Follow the directions of Ukrainian officials and first responders in the event of an emergency

A training session involving some 2,000 Ukrainian conscripts and veterans takes place in the muddy fields of the Champagne military camp in eastern France on Nov. 14. (REUTERS/John Irish)

This comes after Ukraine fired American-supplied long-range missiles into Russia on Tuesday, marking the first time for Kyiv to do so in the 1,000 days of war, which was authorized by President Biden on Sunday.

BIDEN AUTHORIZES UKRAINE TO USE US LONG-RANGE MISSILES TO STRIKE INSIDE RUSSIA

It has been over 1,000 days since Russia invaded Ukraine in early 2022, and the conflict remains very active. (Oleksandr Gimanov/AFP via Getty Images)

This was not the first time the embassy has issued a warning of potential danger and a significant attack. 

A similar warning was issued around Ukraine’s Independence Day on Aug. 24. 

CLICK HERE TO GET THE FOX NEWS APP

Russian President Vladimir Putin signed a revised nuclear doctrine on Tuesday, warning that any attack on Russia supported by a country with nuclear power could be grounds for a nuclear response.

Fox News Digital’s Elizabeth Pritchett contributed to this report.