WASHINGTON (AFP) - The United States on Tuesday (Jan 25) warned Belarus that its authoritarian government will also face reprisals if it assists ally Russia in invading neighbouring Ukraine.

"We've also made clear to Belarus that if it allows its territory to be used for an attack on Ukraine, it would face a swift and decisive response from the United States and our allies and partners," State Department spokesman Ned Price told reporters.

"If an invasion were to proceed from Belarus, if Russian troops were to permanently station on their territory, Nato could well have to reassess our own force posture in the countries that border Belarus," Price said.

The longtime strongman of Belarus, Alexander Lukashenko, is an ally of Russian President Vladimir Putin and has put down mass protests that question the legitimacy of his election.

Lukashenko last month announced that Russia will conduct military exercises with Belarus, leading the United States to warn that nuclear weapons could enter the country.

The move comes as Russia stations tens of thousands of troops on its borders with Ukraine, leading to Western warnings against an invasion of the Western-oriented country.