Russia's air force held scheduled patrol flights at the borders of its ally Belarus on Thursday, Minsk said, as concerns remain that it could take a more active role in the Ukraine war.

Russia has deployed an enhanced task force of 9,000 troops and hundreds of pieces of military hardware to its neighbour after President Alexander Lukashenko said last week Belarus was at threat of attack from Ukraine.

"Right now, the Russian aviation component of the regional troop grouping is carrying out a scheduled patrol of the air borders of the Union State," Belarus' defence ministry said in a statement. The "Union State" is the name of a borderless customs-free zone between Russia and Belarus.

Russia used Belarus as a staging post for its Feb. 24 invasion of Ukraine, deploying troops and equipment from there for its failed offensive on Kyiv in the early days of the war.

Belarus shares a 675-mile (1,085-kilometre) border with Ukraine and is less than 60 miles (100 kilometres) from the Ukrainian capital at its closest point.

While Lukashenko has repeatedly claimed Belarus is at risk of attack by Kyiv, he has so far not sent forces to fight alongside Russia, despite Ukrainian and Western concerns it may.

Ukraine denies it is a threat to Belarus. (Reporting by Reuters; Editing by Andrew Cawthorne)