Russia will station tactical nuclear weapons in Belarus, President Vladimir Putin said on Saturday, sending a warning to NATO over its military support for Ukraine and escalating a standoff with the West.

Although not unexpected and while Putin said the move would not violate nuclear non-proliferation promises, it is one of the Russia's most pronounced nuclear signals since the beginning of its invasion of Ukraine 13 months ago.

Putin likened his plans to the U.S. stationing its weapons in Europe and said that Russia would not be transferring control to Belarus. But this could be the first time since the mid-1990s that Russia were to base such weapons outside the country.

The United States - the world's other nuclear superpower - has reacted cautiously to Putin's statement, with a senior administration official saying there were no signs Moscow planned to use its nuclear weapons.

Reactions continue on Vladimir Putin’s announcement Russia will station tactical nuclear weapons in Belarus.

“It’s a very significant move,” Nikolai Sokol, a senior fellow at the Vienna Center for Disarmament and Non-Proliferation, told Reuters.

“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.”

Putin did not specify when the weapons would be transferred to Belarus, which has borders with three NATO members - Poland, Lithuania, and Latvia. He said Russia would complete the construction of a storage facility there by 1 July.

“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.

The International Campaign to Abolish nuclear weapons called Putin’s announcement on an extremely dangerous escalation.

“In the context of the war in Ukraine, the likelihood of miscalculation or misinterpretation is extremely high. Sharing nuclear weapons makes the situation much worse and risks catastrophic humanitarian consequences,” it said on Twitter.

The senior US administration official noted that Russia and Belarus had been speaking about the transfer of nuclear weapons for some time.

“We have seen reports of Russia’s announcement and will continue to monitor this situation,” the US defense department’s press office said in a written statement.

“We have not seen any reason to adjust our own strategic nuclear posture, nor any indications Russia is preparing to use a nuclear weapon. We remain committed to the collective defense of the NATO alliance” the US said.