Russian President Vladimir Putin said on Thursday that there was nothing unusual in a planned exercise involving the practice deployment of tactical nuclear weapons in southern Russia along with ally Belarus, as preparations for the drills have begun.

Russia said on Monday it would practice the deployment of tactical nuclear weapons as part of a military exercise after what Moscow said were threats from France, Britain and the US. “There is nothing unusual here, this is planned work,” state news agency Tass reported Putin as saying. “It is training.”

Russia’s defence ministry, in its announcement on Monday, explicitly linked the nuclear exercise to “provocative statements and threats by certain western officials against the Russian Federation”.

Putin said last year that Moscow had transferred some tactical nuclear weapons to Belarus, Russia’s first move of such warheads outside Russia since the 1991 fall of the Soviet Union.

Putin said that he had suggested to Belarus that it take part in one of the parts of the nuclear exercise announced on Monday.

“We hold them regularly,” Putin said. “This time they are held in three stages. At the second stage, Belarusian colleagues will join our joint actions.”

“Corresponding instructions have been given to the ministries of defence and the general staffs of our armies. They began joint preparations,” Putin said according to the Kremlin readout, which was earlier cited by Interfax news agency.

Belarusian President Alexander Lukashenko, speaking alongside Putin, said that this was the third such training exercise. “There were probably dozens in Russia, so we synchronized. And the general staffs, as the Russian defence minister told me, have already begun to execute these instructions,” Lukashenko said.

Russia and the US are by far the world’s biggest nuclear powers, holding more than 10,600 of the world’s 12,100 nuclear warheads. China has the third-largest nuclear arsenal, followed by France and Britain.

Russia has about 1,558 non-strategic nuclear warheads, according to the Federation of American Scientists, though there is uncertainty about exact figures for such weapons because of a lack of transparency.

There is still much uncertainty among arms control experts about what weapons Russia has supplied to Belarus and the nature of their storage.

Typically, it would take some time to create the storage, security and barracks for such a deployment — and Russian nuclear weapons are controlled by the Russian defence ministry’s 12th Main Directorate (known as 12th GUMO). It is unclear if the 12th GUMO is in Belarus. No power has used nuclear weapons in war since the US unleashed the first atomic bomb attacks on the Japanese cities of Hiroshima and Nagasaki in 1945.