Britain has dismissed claims that it was "militarising" the Falklands dispute by deploying nuclear weapons nearby.
Argentina said it had intelligence that a Vanguard submarine had been sent to the area, and demanded to know whether it was carrying warheads.
"Thus far the UK refuses to say whether it is true or not," foreign minister Hector Timerman told a press conference. "Are there nuclear weapons or are there not? The information Argentina has is that there are these nuclear weapons."
The accusation, made through a translator, came as Mr Timerman urged the United Nations to intervene in the long-running row over the islands.
He said Britain was using an "unjustified defence of self-determination" to maintain a military base on the Falklands, which allowed it to dominate the Atlantic. "It is perhaps the last refuge of a declining empire," he told journalists in New York. "It is perhaps the last ocean that is controlled by the UK."
He said Britain had been "colonialist throughout (her) history", and should now follow the advice of Beatles legend John Lennon and "give peace a chance".
At a separate press conference immediately afterwards, Britain's ambassador to the UN, Sir Mark Lyall Grant said the Government did "not comment on the disposition of nuclear weapons, submarines etc". But he branded the idea that the UK was "militarising" the situation "manifestly absurd".
Sir Mark said the UK had been in the Falklands since before Argentina existed, and the islanders were entitled to self-determination under the UN charter. "Before 1982 there was a minimal defence presence in the Falkland Islands," he said. "It is only because Argentina illegally invaded the Falkland Islands in 1982 that since then we had to increase our defence posture. Nothing has changed in that defence posture in recent months or recent years."
Tensions between the two nations have been growing over recent months, with David Cameron and Argentine president Cristina Kirchner trading barbs.
The UK has insisted that the deployment of one of its most modern destroyers, HMS Dauntless, to the region is merely routine. The Duke of Cambridge's arrival in the Falklands for a posting as as an RAF search and rescue pilot has further infuriated Buenos Aires.
