"The Kremlin took Belarus as a nuclear hostage," the secretary of Ukraine's National Security and Defence Council, Oleksiy Danilov, wrote on Twitter.

He added that the move was "a step towards the internal destabilization of the country".

On Saturday, Putin said he and strongman Alexander Lukashenko "agreed" Russia would station tactical nuclear weapons in Belarus.

Lukashenko, who has been in power in Belarus for almost 30 years, is a key Putin ally.

Back in February 2022, Minsk allowed the Kremlin to launch its invasion of Ukraine from his country's territory.

Fears have since risen that Belarus may join its ally's offensive, but Lukashenko said he would do so "only if attacked".

For Danilov, Putin's announcement "maximizes the level of negative perception and public rejection of Russia and Putin in Belarusian society".