KYIV, Ukraine — The U.S. Embassy in Kyiv has issued a notification regarding a potential significant air strike by Russia scheduled for Wednesday, prompting the embassy to close its doors as a safety measure.

In an official announcement, the embassy advised its staff to take shelter and urged American citizens residing in Kyiv to be ready for immediate sheltering in case an air alert is announced.

This warning stands out due to its particularity, occurring at a time when Russian aerial assaults on Ukraine are increasingly frequent and have become nearly a daily event.

The alert follows a statement from Moscow, which alleged that U.S.-made long-range missiles were utilized in a recent Ukrainian attack that targeted a munitions depot in the Bryansk region, a situation that came about after President Joe Biden approved the use of such weapons.

Russian President Vladimir Putin had warned in September that should Western nations enable Ukraine to launch strikes deep into Russian territory with these long-range systems, it would signify that NATO members, along with the U.S. and European nations, are engaged in warfare against Russia.

“If that is the case,” Putin remarked, “considering the fundamental shift in the nature of the conflict, we will take suitable actions in response to the threats posed to us.”

Recently, Russia has intensified its airstrike operations, executing intricate drone and missile attacks aimed at energy infrastructure as the weather grows colder.