Russia will station tactical nuclear weapons in neighbouring Belarus, President Vladimir Putin said on Saturday, marking the first time since the mid-1990s that Moscow will have based such arms outside the country.
Such a move would not violate nuclear non-proliferation agreements, Mr Putin said, as the US had stationed nuclear weapons on the territory of European allies.
President Alexander Lukashenko has long raised the issue of putting tactical nuclear weapons in Belarus, which borders Poland, Mr Putin said.
"There is nothing unusual here either: firstly, the United States has been doing this for decades. They have long deployed their tactical nuclear weapons on the territory of their allied countries," he said.
"We agreed that we will do the same — without violating our obligations, I emphasise, without violating our international obligations on the non-proliferation of nuclear weapons."
Russia will have completed the construction of a storage facility for the weapons in Belarus by July 1, Mr Putin said. Russia will not be transferring control of the arms to Minsk, he added.
Russia has stationed 10 aircraft in Belarus capable of carrying tactical nuclear weapons, he said.
Experts say the development is significant, since Russia had until now been boasting that unlike the US, it did not deploy nuclear weapons outside its borders.
Belarus has borders with three Nato members — Poland, Lithuania and Latvia.
"This is part of Putin's game to try to intimidate Nato … because there is no military utility from doing this in Belarus as Russia has so many of these weapons and forces inside Russia," said Hans Kristensen, director of the nuclear information project at the Federation of American Scientists.
Mr Putin did not specify when the weapons would be transferred to Belarus.
Russia has stationed 10 aircraft in Belarus capable of carrying tactical nuclear weapons, Mr Putin said. Moscow has already transferred to Belarus a number of Iskander tactical missile systems that can launch nuclear weapons, he added.
"It's a very significant move," said Nikolai Sokol, senior fellow at the Vienna Centre for Disarmament and Non-Proliferation. "Russia had always been very proud that it had no nuclear weapons outside its territory. So, now, yes, they are changing that and it's a big change."
When the Soviet Union collapsed in 1991, nuclear weapons were deployed in the four newly independent states — Russia, Ukraine, Belarus and Kazakhstan.
In May 1992, the four states agreed all the weapons should be based in Russia and the transfer of warheads from Ukraine, Belarus and Kazakhstan was completed in 1996.