Russian President Vladimir Putin has announced plans to station tactical nuclear weapons in neighbouring Belarus.
It marks a warning to the West as it steps up military support for Ukraine.
Mr Putin said he is responding to Britain’s decision this week to give Ukraine armour-piercing rounds containing depleted uranium.
Russia falsely claimed the rounds have nuclear components.
Mr Putin subsequently toned down his language but insisted in a state television interview broadcast on Saturday night that the ammunition poses an additional danger to troops and civilians in Ukraine.
Tactical nuclear weapons are intended for use on the battlefield, unlike more powerful, longer-range strategic nuclear weapons.
Russia plans to maintain control over the ones it gives to Belarus, and construction of storage facilities for them will be completed by July 1, Mr Putin said.
Mr Putin did not say how many nuclear weapons Russia will keep in Belarus.
The US government believes Russia has about 2,000 tactical nuclear weapons, which include bombs that can be carried by tactical aircraft, warheads for short-range missiles and artillery rounds.
In his interview, Mr Putin said by deploying its tactical nuclear weapons in Belarus, Russia is following the lead of the United States, noting the US has nuclear weapons based in Belgium, Germany, Greece, Italy, the Netherlands and Turkey.
“We are doing what they have been doing for decades, stationing them in certain allied countries, preparing the launch platforms and training their crews,” Mr Putin said.
“We are going to do the same thing.”
Russia has stored its tactical nuclear weapons at dedicated depots on its territory, and moving part of the arsenal to a storage facility in Belarus will up the ante in the Ukrainian conflict by placing them closer to Russian aircraft and missiles already stationed there.
Mr Putin said Belarusian President Alexander Lukashenko has long asked for the nuclear weapons as a counter to Nato.
Belarus shares borders with three Nato members — Latvia, Lithuania and Poland — and Russia used its territory as a staging ground to send troops into Ukraine on February 24 2022.
Mr Putin noted that Russia helped modernise Belarusian military aircraft last year to make them capable of carrying nuclear warheads.
He said 10 such planes are ready to go.
He said nuclear weapons could also be launched by the Iskander short-range missiles that Russia provided to Belarus last year.
Belarusian opposition leader Sviatlana Tsikhanouskaya, who is living in exile, said the agreement to transfer the tactical nuclear weapons to Belarus “underlines the threat to regional security” from Mr Lukashenko’s regime.
“Europe won’t be safe until Belarus dictator is removed & brought before tribunal to face justice for crimes against our country & Ukraine,” Mr Tsikhanouskaya wrote in English on Twitter.
While discussing in his state TV interview the depleted uranium rounds that Britain has promised to ship to Ukraine, Mr Putin alleged the ammunition would leave a radioactive trace and contaminate agricultural land.
“Those weapons are harmful not just for combatants but also for the people living in those territories and for the environment,” he said.
Mr Putin said Russia has vast stockpiles of similar ammunition but so far has refrained from using them.
Depleted uranium is a byproduct of the uranium enrichment process needed to create nuclear weapons.
The rounds cannot generate a nuclear reaction but they do emit low levels of radiation.
The UN nuclear watchdog has warned of the possible dangers of exposure.
Such rounds were developed by the US during the Cold War to destroy Soviet tanks, including the T-72 tanks Ukraine now faces in its push to break through a stalemate in the east.