Russia has taken issue with the deployment of thousands of U.S. troops to Eastern Europe.

The deployments are part of "continuous [NATO] troop rotations," CNN reports, but Moscow nonetheless sees the action as a "threat," the Kremlin said on Thursday.

Rose Gottemoeller, the NATO deputy secretary-general, told the Baltic News Service that the deployment of U.S. troops in Poland is a "proportionate and measured" move.

"We see it as a threat to us," Kremlin spokesman Dmitri Peskov said. "This is an action that threatens our interests, our security, moreover, this is a third nation [apart from Russia and Poland] that is increasing its military presence near our borders in Europe, and it's not even a European nation."

The Associated Press reports that this is first deployment of U.S. troops in Poland "since the fall of communism in 1989." Goettemoeller admitted Moscow is "concerned about what NATO is doing."

But the NATO official did not "see an immediate threat of Russian incursion into NATO spaces" and said she has "some" interest in dialogue .

The maneuvers come as Russia, its geopolitical role, and its effect on the U.S. election, have taken center stage in the confirmation hearings of President-elect Donald Trump's Cabinet nominees, particularly ones in the realms of foreign affairs and national security.

Rex Tillerson, the secretary of state pick, was pressed hard by Sen. Marco Rubio, R-Fla., on Wednesday to label Russian President Vladimir Putin a "war criminal" for his intervention in Syria.

"I would not use that term," Tillerson replied. Rubio says he's undecided in supporting the nominee, and could hold a critical vote that decides Tillerson's passage.

But on Thursday, State Department brass backed up Tillerson's assessment.