A Kremlin spokesman said it would be up to Washington to choose which of its diplomatic staff in Russia would be cut after Russia demanded that it reduce 755 staff members in response to new US sanctions.
Dmitry Peskov said that Russian citizens working for the United States embassy could be among the 755 staff to go, as well as US diplomats.
Moscow did not wait until President Donald Trump signs the new sanctions into law because "there was no point in waiting" after the legislation was adopted in Congress, Mr Peskov said.
The United States has described the decision by Russia as "regrettable" a State Department official said.
"This is a regrettable and uncalled for act," the official said.
"We are assessing the impact of such a limitation and how we will respond to it."
Moscow ordered the United States on Friday to cut hundreds of diplomatic staff and said it would seize two US diplomatic properties after the US House of Representatives and the Senate overwhelmingly approved new sanctions on Russia.
The White House has said President Trump would sign the sanctions bill.
Russian President Vladimir Putin said in an interview with Vesti TV released yesterday that the United States would have to cut its diplomatic and technical staff by 755 people by 1 September.
"Because more than 1,000 workers - diplomats and support staff - were working and are still working in Russia, 755 must stop their activity in the Russian Federation," he said.
The new US sanctions were partly a response to conclusions by US intelligence agencies that Russia meddled in the 2016 US presidential election, and to punish Russia further for its annexation of Crimea from Ukraine in 2014.
A federal law enforcement investigation and multiple US congressional probes looking into the possibility that Mr Trump's campaign colluded with Russia have made it harder for Mr Trump to open a new chapter with Mr Putin.
Russia denies it interfered in the election and Mr Trump has said there was no collusion.