The risk of a nuclear weapon being used is higher than at any time since the Cold War, a UN official warned on Friday.
Izumi Nakamitsu, the UN's high representative for disarmament, said the absence of dialogue and the weakening of arms control measures are driving risk.
Speaking at a UN Security Council session on Russia's plans to station nuclear weapons in Belarus, Ms Nakamitsu urged Washington and Moscow to avoid any actions that could lead to “escalation, mistake or miscalculation”.
"The risk of a nuclear weapon being used is currently higher than at any time since the depths of the Cold War," she said.
"The war in Ukraine represents the most acute example of some of that risk."
She called on both nations to return to full implementation of the New Start Treaty, after President Vladimir Putin suspended Russian participation in the last remaining nuclear arms control deal with the US.
Signed in 2011, New Start limits each country to no more than 1,550 deployed nuclear warheads and 700 deployed missiles and bombers.
Deputy US Ambassador to the UN, Robert Wood, accused Moscow of “escalating Russia's dangerous and destabilising behaviour” with its threat to send nuclear weapons to Belarus.
"No other country has raised the prospect of potential nuclear use in connection with the war in Ukraine. No other country's increasing nuclear deployments in Europe are issuing implied threats of use,” said Mr Wood.
The US diplomat also called on the Lukashenko regime to “cease its complicity” in Russia's war against Ukraine.
Poland’s UN Ambassador, Krzysztof Szczerski, deplored Minsk’s role as “enabler” and said Moscow's plans to deploy tactical nuclear weapons to Belarus would constitute an “irresponsible escalation” and pose a major risk to the global non-proliferation system.
Russia’s top UN envoy, Vasily Nebenzya, told the Security Council that the Kremlin was not violating its international obligations.
He said the Kremlin “was clear about the fact that we are not transferring nuclear weapons, we're talking about the transfer to Belarus of operational tactical missile complexes.”
In an annual address to government officials on Friday, Belarus President Alexander Lukashenko said Moscow's plans would help protect Belarus, which he alleged was under threat from the West.
On Sunday, Nato called Russia’s nuclear plan “dangerous and irresponsible”.
