Marines will now be among the thousands of U.S. troops who have been deployed to Europe and the eastern edge of the NATO alliance in response to Russia's ongoing invasion of Ukraine.

About 200 Marines from a command-and-control unit for Marine Air Control Group 28 based at Cherry Point, North Carolina, were sent to Lithuania, following a cold weather exercise in Norway, the Pentagon said Tuesday. A couple of Marine Corps C-130 Hercules transport aircraft and 10 Marine F-18 Hornet fighter jets from Beaufort, South Carolina, will be repositioned to Eastern Europe.

The latest deployment comes as Russia appeared to be pulling back and repositioning its invasion forces following weeks of stiff resistance by Ukraine, and the Pentagon claimed Russian President Vladimir Putin had "failed" in his effort to seize the capital Kyiv.

The Pentagon has 14,000 troops already deployed to Europe, positioned with allies such as Poland, Germany and the Baltic states, or on high-alert for possible deployment. On Monday, it announced that six Navy EA-18G Growler aircraft based at Naval Air Station Whidbey Island in Washington state were sent to Spangdahlem Air Base in Germany.

"It's not about a number goal, it's really about capabilities and it's based on constant conversations with our NATO allies on the eastern flank," Pentagon spokesman John Kirby said during a briefing on Tuesday.

The Marine and Navy deployments were done unilaterally by the U.S. and were not part of the NATO Response Force, which is an elite multinational force of 40,000 troops that includes the U.S. and was recently activated by the alliance.

Ukrainian officials said the bodies of hundreds of civilians had been found in towns around the capital Kyiv after Russian troops withdrew.

The images of handcuffed corpses lying face down in the streets or hastily dug graves in Bucha unleashed a wave of outrage, with European leaders joining Ukrainian President Volodymyr Zelenskyy in calling it a genocide.

Russian Foreign Minister Sergey Lavrov rejected the allegations, describing the scenes outside Kyiv as a “stage-managed anti-Russian provocation”.

Poland’s Prime Minister Mateusz Morawiecki described Russia as a “totalitarian-fascist state," saying “the bloody massacres perpetrated by Russian soldiers deserve to be called by name: This is genocide." Spain's Prime Minister Pedro Sánchez also used the word “genocide,” saying those responsible should answer for their crimes.