Russian President Vladimir Putin has said the United States would have to cut its embassy and consulate staff in Russia by 755 under new sanctions from Moscow.
In response, the US State Department deemed it "a regrettable and uncalled for act."
Russian's Foreign Ministry on Friday ordered a reduction by Sept 1 in the number of US diplomatic personnel in Russia.
It said it is ordering the US Embassy to limit the number of embassy and consular employees in the country to 455 in response to approval of a new package of sanctions by the US Congress. The White House has said US President Donald Trump would sign those sanctions into law.
"We had hoped that the situation will somehow change, but apparently if it changes, it won't be soon," Putin said in an interview televised on Rossiya 1, explaining why Moscow decided to retaliate. "I thought it was the time to show that we're not going to leave it without an answer."
Russia is open to cooperating with the US on various issues, including terrorism and cybercrime, but instead it "only hears unfounded accusations of meddling in US domestic affairs," he said.
Putin said more than 1,000 people are currently employed at the Moscow embassy and three US consulates in Russia. They include both Americans and Russians hired to work in the diplomatic offices.
The Russian leader did not explain how the figure of 755 positions was calculated.
In a statement, the State Department said: "This is a regrettable and uncalled for act. We are assessing the impact of such a limitation and how we will respond to it. We have no further comment at this time."
The State Department declined to give an exact number of American diplomats or other US officials in Russia, but the figure is believed to be about 400, some of whom have families accompanying them on diplomatic passports.
The vast majority of the more than 1,000 employees at the various US diplomatic missions in Russia, including the embassy in Moscow and consulates in St Petersburg, Vladivostok and Yekaterinburg, are local employees.
Asked about the potential for additional sanctions against Washington, Putin described the reduction in diplomatic staff as "painful" and said he currently opposes further measures.
"We certainly have something to respond with and restrict those areas of joint cooperation that will be painful for the American side, but I don't think we need to do it," he said, adding that such steps could also harm Russian interests.
Putin mentioned space and energy as the main areas where Russia and the United States have successfully pursued projects together.
Along with the cap on the size of the US diplomatic corps in Russia, the Russian foreign ministry on Friday said it also was closing down a US recreational retreat on the outskirts of Moscow as well as warehouse facilities.
The diplomatic tit-for-tat started under former US President Barack Obama. In response to reports of Russian meddling in the 2016 presidential election, Obama ordered the expulsion of 35 Russian diplomats and shut down two Russian recreational retreats in the US.