Russia has expelled the US deputy chief of mission to Russia, Bart Gorman, a State Department spokesperson said on Thursday, warning of a US response amid heightened fears of a Russian invasion of Ukraine.
"Russia's action against our DCM was unprovoked and we consider this an escalatory step and are considering our response," the spokesperson said.
It was not immediately clear what justification Moscow gave for the expulsion, but it comes during a months-long standoff over a Russian buildup of more than 150,000 troops near its border with Ukraine.
US officials warned the risk of a Russian invasion remained high and that Russia may attempt to fabricate a pretext for a conflict, despite Moscow saying it was moving some of its troops away from the border.
Alongside the border tensions, the United States and Russia have been engaged in a tussle over their respective diplomatic presences in each others' capitals and Moscow said in December that US Embassy staff who have been in the post for more than three years should return home.
The spokesperson said Gorman, the second most senior US official at the US Embassy in Moscow, had a valid visa and had been in Russia for less than three years.
"We call on Russia to end its baseless expulsions of US diplomats and staff and to work productively to rebuild our missions," the State Department spokesperson said. "Now more than ever, it is critical that our countries have the necessary diplomatic personnel in place to facilitate communication between our governments. "