"A snap check of combat readiness has begun," the ministry said, adding it was ordered by Belarusian leader Alexander Lukashenko.

Troops would have to get to "designated areas" as fast as possible, the ministry said.

They would be tasked to "organise security and defence and build bridge crossings across the Neman and Berezina rivers".

The Neman river runs in central Belarus and along the Polish border. The Berezina river flows east of the capital Minsk.

The defence ministry said it planned to move military equipment and personnel, which would "temporarily restrict the movement of citizens... along certain public roads and terrain".

Lukashenko, who has been in power since 1994, is a long-time ally of the Kremlin.

Russian troops crossed into Ukraine from several directions on February 24, including from Belarusian territory.

Before launching its offensive, Moscow held military exercises in Belarus.

Kyiv has since bolstered its defence on its northern border with Belarus and Russia.

But Lukashenko has repeatedly said he does not plan to send Belarusian troops to Ukraine.