Soldiers from units such as the 82nd Airborne Division and the 101st Airborne Division are among the 8,500 troops who are on heightened alert over rising tensions in Europe.

Also on alert are elements of the XVIII Airborne Corps and the 4th Infantry Division, as well as additional units from Fort Campbell, Kentucky; Fort Hood, Texas; Joint Base Lewis-McChord, Washington; Fort Polk, Louisiana; and Fort Stewart, Georgia, Pentagon Spokesman John Kirby said Jan. 27.

“These units, all told, include medical support, aviation support, logistics support and, of course, combat formations,” Kirby said. He did not provide additional details.

The Pentagon on Jan. 24 announced that up to 8,500 U.S. troops have been put on heightened alert as tensions continue to rise over fears of a Russian invasion of Ukraine. 

If activated, the troops would support the NATO Response Force, Kirby said at the time. The alert allows for the units to prepare to move quickly if needed, Kirby said.

On Jan. 27, Kirby again stressed that the troops were on alert only. “These forces are on a heightened preparedness to deploy,” he said. “They have not been activated.”

The NATO Response Force is a multinational force made up of land, air, maritime and special operations forces that the alliance can deploy quickly, wherever needed, according to the NATO website. The force is about 40,000 strong, and the U.S. contributes to the force along with other NATO nations, Kirby said.

Any decision to activate the NATO Response Force must be made by the alliance, he said.

Tensions in Europe have soared over concerns that Moscow is planning to invade Ukraine, the Associated Press reported. Russia, which has denied is it planning an invasion, has massed about 100,000 troops near Ukraine’s border, according to AP, and demanded, among other things, that NATO promise it will never allow Ukraine to join the alliance.