The United States will deploy 2,000 troops to Poland and Germany this week and reposition about 1,000 soldiers based in Germany to Romania as concerns mount over a possible Russian invasion of Ukraine.

The Pentagon on Wednesday announced that U.S. President Joe Biden had formally approved the additional deployments with officials adding they would happen in the "coming days".

Pentagon press secretary John Kirby said the deployments were not permanent and stressed that those troops "are not going to fight in Ukraine".

"It's important that we send a strong signal to Mr. Putin and to the world" Kirby said.

Meanwhile, a further 8,500 troops in the U.S. have been put on higher alert for potential deployment to Europe as additional reassurance to U.S. allies.

The U.S. and other Western counties have expressed concern over a buildup of Russian troops on the border with Ukraine, alleging that Russia is planning an invasion of its neighbor.

Though Ukraine is not a member of NATO, the U.S. is worried about a possible spillage into neighboring NATO countries if Russia does indeed attack Ukraine.

Russia maintains it does not plan to invade Ukraine and has demanded a number of security guarantees from NATO, including a promise that Ukraine will not join the military alliance.

The other demands by Russia are that NATO does not deploy weapons near the Russian border and rolls back its forces from Eastern Europe.

Talks between Russia and the West have been initiated to try and defuse the situation but have so far failed to yield any progress.

(With input from agencies)