Deputy Prime Minister Nick Clegg has said "insinuations" by Argentina that the UK sent a nuclear-armed submarine to the South Atlantic are "baseless".
Tensions have been rising in recent months between the two countries over the future of the Falkland Islands.
Argentine Foreign Minister Hector Timerman reportedly told a summit that an "extra-regional power" had sent the submarine to the area.
Mr Clegg said Argentina seemed "keen to rattle cages in any way they can".
It is the latest development in an ongoing argument between the UK and Argentina as the 30th anniversary of the Falklands War approaches.
Mr Clegg and Mr Timerman are both attending the international nuclear security summit in the South Korean capital, Seoul.
It was reported last month that the UK had deployed a nuclear-powered but conventionally armed Trafalgar class submarine to the ocean around the Falklands - something the Ministry of Defence has refused to confirm or deny.
However, Mr Timerman subsequently told 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.
British officials said Mr Timerman had repeated the allegation at the meeting in Seoul, referring to an "extra-regional power" which had deployed a submarine "capable of carrying nuclear weapons" in the South Atlantic.
In his address to the conference, Mr Clegg said he was "duty-bound to respond to the insinuations made by the Argentinean delegation of militarisation of the South Atlantic by the British government".
"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."
The status of the Falklands, known in Argentina as the Malvinas, is still a highly sensitive issue for Buenos Aires.
It has called on the UK to enter into negotiations over the islands' future - something Britain has refused to do.
After his address, Mr Clegg told the BBC it was "inappropriate" of the Argentines to "crowbar" a complaint about the UK into the summit.
He said the government's position was "crystal clear" on the treaty.
"I provided that explanation to the Argentine representatives, but I get the impression they are keen to rattle cages in any way they can, which is unfortunate because the issue of sovereignty, as far as the Falklands is concerned, is settled."
David Cameron has insisted the Falklands will remain British as long as the people living there want them to.
The UK has sent HMS Dauntless, one of its largest and most powerful air defence destroyers, to the South Atlantic, but says it is only carrying out routine operations and the warship is only replacing one in the area.
Meanwhile, the UK is to share details of previously classified technology in an attempt to prevent terrorists acquiring a nuclear device or radiological "dirty bomb".
Mr Clegg disclosed that cutting-edge devices had been used at UK borders since 2001, while in recent years the government had developed specialist teams to respond to the threat of an improvised suitcase bomb.
Sharing would allow countries around the world to "raise our game" in fighting terrorism, he told the Seoul conference.
In: Regional News
Tags: argentina, britain, falklands, submarine, nuclear, weapons, vanguard, trafalgar, treaty, tlatelolco
Location: Argentina (load item map)
Marked as: approved
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