The United States temporarily closed its embassy in Kyiv on Wednesday, citing credible intelligence of a potential significant air attack as tensions escalate in the Russia-Ukraine war.

In a statement posted on the embassy’s website, the U.S. Department of State Consular Affairs announced the precautionary closure and directed embassy staff to shelter in place. The embassy also urged American citizens in Ukraine to remain vigilant and be prepared to seek immediate shelter if air alerts are issued.

The warning comes just days after Ukraine deployed U.S.-supplied Army Tactical Missile Systems (ATACMS) to strike targets in Russian-held territory, a development facilitated by outgoing U.S. President Joe Biden’s authorization. This milestone coincided with the war’s 1,000th day, intensifying geopolitical tensions.

Russia has long cautioned that Western nations’ support for Ukrainian strikes on Russian soil could lead Moscow to view NATO members, including the United States, Britain, and France, as direct participants in the conflict.

Russian President Vladimir Putin had previously warned of retaliatory actions against Ukrainian operations conducted with U.S.-made weapons inside Russia. On Tuesday, Putin escalated the stakes by revising Russia’s nuclear doctrine to allow nuclear retaliation against a broader range of conventional attacks, further raising the specter of nuclear confrontation.

This development marks one of the gravest escalations since the conflict began, pushing U.S.-Russia relations to their lowest point in decades and exacerbating global concerns over a potential escalation into a broader war.

The situation remains fluid, with the United States and its allies closely monitoring the unfolding crisis.