U.S. President Joe Biden approved on Wednesday the deployment of additional troops to NATO members Germany, Poland and Romania as tensions with Russia over Ukraine remain high over the security bloc's expansion in Eastern Europe.

About 2,000 troops from Fort Bragg, North Carolina, will be deployed to Poland and Germany this week while part of an infantry Stryker squadron of roughly 1,000 troops based in Germany will be deployed to Romania, a senior administration official said.

The military moves come amid stalled talks with Russia over its military buildup at Ukraine’s borders. They also underscore growing fears across Europe that Russian President Vladimir Putin is poised to invade Ukraine – with smaller NATO countries on the eastern flank worry they could be next.

The official spoke on the condition of anonymity to discuss military moves not yet announced.

The U.S. military last week put about 8,500 troops on alert to be ready to deploy to Europe if needed, potentially on very short notice, in the latest effort to reassure jittery NATO allies in the face of a Russian military buildup near Ukraine.

The U.S. troops notified of ready-to-deploy orders last week included additional brigade combat teams, logistics personnel, medical support, aviation support, and troops forces involved with intelligence, surveillance and reconnaissance missions.