The Biden administration is considering sending as many as 5,000 U.S. troops to Eastern Europe, a U.S. official confirmed to NPR, in what would be a step-up in American military involvement in the region amid growing fears of a Russian invasion of Ukraine.

U.S. troops could be headed to Romania and Poland, or possibly Bulgaria or Hungary. No final decision has been made but the troops have been told to be ready to move, the official said.

U.S. service members could be drawn from their existing posts elsewhere in NATO countries in Europe. Some of the troops would also likely come from the 82nd Airborne Division at Fort Bragg, N.C.

The New York Times, which first reported the news of planned troop movements, said senior Pentagon officials laid out a number of options for President Biden on Saturday.

Among them, sending 1,000 to 5,000 troops to Eastern European countries and the Baltics, "with the potential to increase that number tenfold if things deteriorate," according to the Times.

There are no plans to send more Americans into Ukraine itself, according to the paper.

The Biden administration has held back on more aggressive actions, for fear of inciting a Russian invasion.

So far, U.S. aid to Ukraine has largely come in the form of military equipment. A Biden administration shipment of aid — close to 200,000 pounds of "lethal aid" including ammunition — arrived in Ukraine on Friday. In October, the U.S. sent Ukraine 30 Javelin anti-tank guided missile systems.

There are already more than 150 U.S. military advisers in Ukraine, the Times reported, though they are far from any potential front lines and would likely leave the country quickly after a Russian invasion.

Last week, Biden said he had warned Russian President Vladimir Putin that his country's invasion of Ukraine would cause Washington to send more troops to the region.

"We're going to actually increase troop presence in Poland, in Romania, et cetera, if in fact he moves," Biden said in a news conference, pointing out that the two countries are NATO members.

Ukraine is not a NATO member, and Russia has demanded that it never become one.

Russia has stationed more than 100,000 troops near the Ukraine border, raising fears of an imminent assault on the country. Russia has rejected that it has such plans in store.

While Ukraine boasts mighty military power, Russia's bigger, more modern army would likely give it the upper hand should the country invade.

The State Department earlier Sunday ordered the departure of diplomats' families from Ukraine, in a move that officials assured did not signify waning support for the country.

Tom Bowman contributed reporting.

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