Russia has expelled US Deputy Ambassador Bart Gorman, one of the top American diplomats at the US Embassy in Moscow, the Russian RIA Novosti and TASS news agencies reported.
The US is reportedly preparing to respond in kind.
The move comes as the tense standoff over Russia's aggressive actions towards Ukraine continue Thursday.
US and NATO sources have said that the Russian military forces stationed near the Ukrainian border have not decreased despite claims by Russia that some of its forces had been returned to base.
NATO Secretary-General Jens Stoltenberg said at a regular meeting of defense ministers in Brussels that his organization had "the ability to prove through satellite images that Russia had not withdrawn its forces from Ukraine. What we are seeing is that they have increased the number of their troops, and more forces are on the way, If they really start to retreat, that's something to be grateful for and we welcome this, but they've always moved forces back and forth."
Meanwhile, Russia's Investigative Committee claims that mass graves of hundreds of Russian-speaking civilians had been found in the Donbas region, and the Russian government is accusing Ukraine of genocide.
The Russian news agency RIA reported that Ukrainian forces were the first to open fire, when representatives of the "People's Republic of Luhansk," a group of rebels allegedly supported by the Russians, claimed that the Ukrainian army opened fire on them and used machine guns and grenades against them. "Ukraine's military forces have grossly violated the ceasefire, using military weapons," Maariv reported Luhansk representatives saying.
NATO responded to the Russian claims by saying that Russia is attempting to create a pretext to invade Ukraine.
“We are concerned that Russia is trying to stage a pretext for an armed attack against Ukraine, there is still no clarity, no certainty about the Russian intentions,” Stoltenberg said.
UK Prime Minister Boris Johnson also accused Russia of a "false flag operation designed to discredit the Ukrainians."