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.”

“Out of an abundance of caution, the Embassy will be closed, and Embassy employees are being instructed to shelter in place,” it said in a security alert, recommending U.S. citizens take shelter if an air alert is announced.

Shutting the embassy is not an unprecedented move amid the war, which reached its 1,000th day Tuesday.