The Christian Campaign for Nuclear Disarmament (CND) has expressed concern at Vladimir Putin's threats to "use all the means at our disposal" in Russia's war with Ukraine.
The Russian president's comments on Wednesday have been widely interpreted as a threat to use nuclear weapons.
"It is not a bluff," Putin warned.
Bridget Tiller, Co-chair of Christian CND, said that Putin's comments must spur international efforts towards nuclear disarmament.
She called on Putin to engage in peace talks with Ukraine.
"Vladimir Putin's continued threats to use nuclear weapons demonstrate the very real threat that they pose to our world - and highlights the urgency of the task to eliminate them," she said.
"The vast majority of states do not feel the need to conduct relations with the threat of annihilation. We hope this latest episode will spur further movements towards nuclear disarmament for our shared security.
"The war in Ukraine is causing enormous suffering and will only end through a negotiated settlement.
"We pray that rather than threatening more destruction, Putin would instead engage in meaningful peace talks to bring the conflict to an end."
In an address to the UN, British Prime Minister Liz Truss dismissed Putin's threat as "sabre-rattling" and insisted that it would "not work".
"This morning we have seen Putin trying to justify his catastrophic failures," she said.
"He is doubling down by sending even more reservists to a terrible fate. He is desperately trying to claim the mantle of democracy for a regime without human rights or freedoms.
"And he is making yet more bogus claims and sabre-rattling threats. This will not work."
Putin's threat coincides with the call-up of 300,000 reservist troops to support Russia's faltering campaign in Ukraine.
The US is reported to have secretly warned Russia of dire consequences if it carries out a nuclear strike in Ukraine.