WASHINGTON, 31. Jan (REUTERS) -- The Pentagon said on Monday (Jan 31) that it is in active discussions with Eastern European allies about possible United States troop deployments to the North Atlantic Treaty Oranization's (NATO) eastern flank, as Washington moves to reassure jittery NATO allies in the face of a Russian military build-up near Ukraine.

Any decisions on new troop movements would be separate from the 8,500 forces in the US who were put on alert last week to potentially bolster a NATO rapid response force, the Pentagon said, adding context to President Joe Biden's comments last Friday about potential near-term deployments to Eastern Europe.

Pentagon spokesman John Kirby said the troops that Biden was referring on Friday could potentially be redeployed from within Europe.

"We're going through the rigorous work of providing options for the commander in chief should he decide to do that ... in close consultation with the actual allies themselves," Kirby said.

Separately, the US military last week put about 8,500 troops inside the United States on alert to be ready to deploy to Europe, largely to fill the ranks of a NATO rapid response force should the alliance call them up for duty.