WARSAW, 19 Feb (Reuters) - US Defense Secretary Lloyd Austin announced on Friday (Feb 18) the planned sale of 250 Abrams tanks to Poland, as Washington moves to strengthen the defences of a key eastern European ally amid a mounting threat of war between neighboring Ukraine and Russia.

Austin was speaking during a trip to Warsaw, where Polish leaders have been alarmed by the deployment of thousands of Russian forces in neighbouring Belarus, part of a huge Russian buildup around Ukraine that NATO says positions Moscow for an invasion. President Vladimir Putin denies any plan to invade.

"Some of those forces (are) within 321km of the Polish border," Austin said.

"If Russia further invades Ukraine, Poland could see tens of thousands of displaced Ukrainians and others flowing across its border, trying to save themselves and their families from the scourge of war."

The sale of Abrams tanks to Poland, which is also home to a future US missile defense site, is another sign of a deep and growing defence relationship with the United States. It follows the deployment of nearly 5,000 additional US troops to Poland as well as additional fighter aircraft, as part of Washington's response to the Ukraine crisis.