The United States is continuing to reinforce its military forces in Europe as planned, irrespective of President-elect Donald Trump's future intentions, the Pentagon said Thursday.

Trump, who will take office in January, raised serious concerns in Europe by promising during his campaign that US engagement in NATO under his presidency would be conditional on members' payments to the alliance.

Washington is scheduled to start deploying an additional combat brigade in Europe in February to bring the number of brigades on the continent to three.

The plan is part of an effort to boost Eastern European defenses against possible attack by Russia.

"We are executing plans as they were constructed with our NATO allies," Pentagon spokesman Peter Cook said.

"We leave it to the next administration to speak their policy choices," he added. "We have one commander-in-chief at a time."

The new brigade is set to begin its deployment with an exercise in Poland before sending companies to Bulgaria, Romania and the Baltic States.

Trump, who has praised Russian President Vladimir Putin, has criticized President Barack Obama's policy toward Moscow, saying he wants to improve relations.

Asked about the possibility that the current defense secretary, Ash Carter, would remain in office under Trump, Cook declined to comment on what he called "hypothetical" situations.

Carter "is focused on his job right now and he wants to serve this president until the end of his term," he said.