"The first nuclear warheads were delivered to the territory of Belarus... This is the first part," Putin told an annual economic forum, where AFP and media of other countries Russia deems "unfriendly" were not accredited.

The Russian leader had announced the plans to send tactical nuclear weapons -- less powerful than strategic ones -- in March.

"By the end of summer, the end of the year, we will complete the process," of transferring tactical nuclear weapons to Belarus, Putin said.

Tactical nuclear arms are battlefield weapons that, while devastating, have a smaller yield compared to long-range strategic weapons.

Belarusian leader Alexander Lukashenko has allowed his territory -- which borders Ukraine as well as EU and NA members Poland and Lithuania -- to serve as a launch pad for Russia's Ukraine offensive.

Putin's announcement had spurred fears of nuclear conflict, but experts and governments said it was unlikely it would change the course of the conflict.

Putin said the weapons were meant as deterrence to "those who are thinking of inflicting a strategic defeat on Russia".

Belarusian troops began training on nuclear-capable Russian missile systems in April.