The United States has reacted cautiously to Russia's decision to place nuclear weapons in Belarus.
On Saturday it was reported by a Russian news agency that Vladimir Putin has signed a deal to station tactical nuclear weapons in Belarus.
Ten aircraft capable of carrying the armaments - which are designed for use on the battlefield, rather than to wipe out cities - have reportedly already been moved there.
It is the first time since the mid-1990s that Russia has based such weaponry outside the country.
But a senior US administration official told the Reuters news agency there are no signs Moscow plans to use the weapons.
"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 defence of the NATO alliance."
A top security adviser to Ukrainian President Volodymyr Zelenskyy warned the move would destabilise Belarus.
"The Kremlin took Belarus as a nuclear hostage," Oleksiy Danilov, the head of Ukraine's National Security and Defence Council, wrote on Twitter.
'No violation' of nuclear treaty
Mr Putin claimed the decision would not violate nuclear non-proliferation agreements, as the US already has such weapons stationed in Europe, according to Russian news agency Tass.
This is a reference to an international treaty aimed at preventing the spread of nuclear weapons - keeping them out of the hands of countries that do not already have them.
But Mr Putin has said the weapons to be stationed in Belarus - which does not have nuclear arms - would remain under Russian control.
"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," Mr Putin told state television.
"We agreed that we will do the same - without violating our obligations, I emphasize, without violating our international obligations on the non-proliferation of nuclear weapons."
The US has an estimated 100 nuclear warheads at air bases on the continent, including in Germany, the Netherlands, and Turkey, according to the Centre for Arms Control and Non-Proliferation.
Russia's reliance on Belarus
Tensions have grown over the war in Ukraine after heavy supplies of Western weaponry to Kyiv and Moscow shifting its rhetoric on its military operation away from "demilitarisation" of its neighbour to fighting "the collective West" there.
This latest deal is another sign of the Kremlin's reliance on Belarus as an ally during the war in Ukraine.
Mr Putin and Belarusian President Alexander Lukashenko have both visited each other in their respective capital cities.
Belarus has also helped trained Russian troops, looked after those injured, and provided supplies. The regime has also let Russia use its territory to launch land and air attacks.