An air raid alert was declared in the Ukrainian capital and several other regions on Wednesday amid what Kyiv's air force described as a missile threat.
The alert, which the head of Ukraine's presidential administration urged citizens not to ignore, came just hours after the US State Department closed its Kyiv embassy due to "specific information of a potential significant air attack."
"The US embassy in Kyiv has received information of a potential significant air attack and will be closed," the US Department of State Consular Affairs said in a statement.
"Out of an abundance of caution, the embassy will be closed, and embassy employees are being instructed to shelter in place," the department said in a statement published on the website of the US embassy in Kyiv.
"The US Embassy recommends US citizens be prepared to immediately shelter in the event an air alert is announced."
The warning comes a day after Ukraine used US ATACMS missiles to strike Russian territory, taking advantage of newly granted permission from the outgoing administration of US President Joe Biden on the war's 1,000th day.
Russia had been warning the West for months that if Washington allowed Ukraine to fire US, British, and French missiles deep into Russia, Moscow would consider those NATO members to be directly involved in the war in Ukraine.
A promised response
Russian President Vladimir Putin said in October that Moscow would respond to Ukraine's strikes with US-made weapons deep into Russia.
On Tuesday, Putin lowered the threshold for a nuclear strike in response to a broader range of conventional attacks, with nuclear risks rising amid the highest tensions between Russia and the West in more than half a century.