WASHINGTON (Nexstar) — The Pentagon provided an update Friday on what the U.S. military is doing to prepare in the event that Russia invades Ukraine.

And according to Secretary of Defense Lloyd Austin, putting American combat troops on Ukrainian soil isn’t in the White House’s plans.

Still, thousands of troops based in the U.S. remain on heightened alert this week, ready to deploy to Europe to support America’s NATO allies.

“Ukraine has a border with four NATO members, Poland, Slovakia, Hungary and Romania,” Chairman of the Joint Chiefs of Staff Gen. Mark Milley said.

Pentagon officials said U.S. troops are committed to defending those allies if necessary. Milley said while Ukraine is not a member of NATO, “Ukraine has a right to be independent.”

And the U.S. is actively assisting the Ukrainian military.

“We continue to provide military material support to Ukraine, along with many other countries from NATO,” Milley said.

Milley said the U.S. is providing money and delivering weapons to the Eastern European nation, and a few hundred American troops are already in Ukraine, training, advising and assisting the country’s own military.

“If Russia chooses to invade Ukraine, it will not be cost-free — in terms of casualties or other significant effects,” he said.

Military leaders stressed it’s not too late to avoid a conflict and turn to diplomacy, but they said it’s their job to prepare for any scenario.