The US has expelled two Russian diplomats in response to an attack on an American diplomat in Moscow, the state department says.
Spokesman John Kirby said the two officials - who have not been named - were told to leave on 17 June.
Mr Kirby said that earlier that month, a Russian policeman attacked the US diplomat near the US embassy in Moscow.
"The action was unprovoked," he said. Russia said the diplomat worked for the CIA and had refused to show ID papers.
Last month, US officials said harassment against US diplomats by Russian security and intelligence services was on the rise.
Russia has denied the allegation.
'In disguise'
"On 17 June, we expelled two Russian officials from the United States to respond to this attack," Mr Kirby said on Friday.
He said this was in response to the attack on the US diplomat on 6 June.
The assault happened after the accredited American official had identified himself to the policeman, Mr Kirby said.
"The action was unprovoked and it endangered the safety of our employee. The Russian claim that the policeman was protecting the embassy from an unidentified individual is simply untrue."
Russia said earlier this week that the US official was a CIA agent who had refused to provide his identification papers and hit the policeman in the face.
"Instead of the CIA employee, who was in disguise, as we understand, it could have been anyone - a terrorist, an extremist, a suicide bomber," Russian foreign ministry spokeswoman Maria Zakharova said.
Russian media have also released a video of what they say was the scuffle between the US diplomat and the Russian policeman.
Last month, the US said it had raised the issue of the alleged harassment of US diplomats in Russia directly with President Vladimir Putin.
'Family pet killed'
Washington said the problems began two years ago after the US - as well as the EU - imposed sanctions against Russia over its annexation of Ukraine's southern Crimea peninsula and its ongoing involvement in the conflict in eastern Ukraine.
Specific incidents have not officially been revealed.
But the Washington Post said last month they included breaking into the homes of embassy staff, rearranging furniture and even killing a family pet.
No official response has been made by Russia but a statement to the Post did not deny the charge and said there had been US provocation against Russian diplomats.
The former US ambassador to Russia, Michael McFaul, told the newspaper that while his family was living in Moscow, they were routinely followed by security services that wanted him to know they were being watched.