Britain has denied sending a nuclear-armed submarine to the South Atlantic amid rising tensions with Argentina over the Falklands.
Deputy Prime Minister Nick Clegg dismissed the claims as "baseless insinuations" in a clash with the Argentine foreign minister at the international Nuclear Security Summit in Seoul, South Korea.
The latest spat erupted as British officials were braced for intensifying diplomatic pressure from Buenos Aires in the run-up to the 30th anniversary of the Falklands War.
It was reported last month that the UK had despatched a nuclear-powered but conventionally-armed Trafalgar class submarine to the region - a deployment the Ministry of Defence has refused to confirm or deny.
However, it led to Argentine foreign minister Hector Timerman claiming at the United Nations that Britain had in fact sent a nuclear-armed Vanguard class submarine in violation of the Treaty of Tlatelolco, which guarantees Latin America as a nuclear weapons-free zone.
Despite British denials, officials said Mr Timerman had repeated the allegation at today's meeting in Seoul, referring to an "extra-regional power" which had deployed a submarine "capable of carrying nuclear weapons" in the South Atlantic.
Mr Clegg, who is leading the British delegation at the summit, strongly rejected the claim.
"These are unfounded, baseless insinuations," he said.
"As I'm sure our colleague from Argentina knows, the United Kingdom ratified the protocols to the treaty in 1969 ... which guarantees a nuclear weapons-free zone covering Latin America and the Caribbean.
"We have respected those obligations since 1969 and we will continue to do so."