Argentina has accused Britain of deploying nuclear weapons near the Falkland Islands and "militarising" the south Atlantic.

The Argentinian foreign minister, Héctor Timerman, lodged a formal protest at the United Nations on Friday and showed slides of British military bases in the region, saying they represented a threat to all south America.

He said Buenos Aires had intelligence that a Vanguard submarine was operating in the area. "Thus far the UK refuses to say whether it is true or not," he told a press conference in New York. "Are there nuclear weapons or are there not? The information Argentina has is that there are these nuclear weapons." Quoting John Lennon, he added: "Give peace a chance."

Britain's ambassador to the UN, Mark Lyall Grant, said London did not comment on the disposition of nuclear weapons or submarines but that it was "manifestly absurd" to say it was militarising the region. Britain's defence posture remained unchanged, he said.

The Daily Mail reported this week that Britain had deployed a Trafalgar-class nuclear-powered submarine armed only with conventional weapons.

Timerman said such a nuclear-armed submarine would violate the Treaty of Tlatelolco for the Prohibition of Nuclear Weapons in Latin America and the Caribbean.

After receiving Timerman's protest the UN secretary general, Ban Ki-moon, issued a statement expressing "concern" about the escalating row and reportedly offered to mediate.

Argentina's president, Cristina Fernández de Kirchner, said Britain's dispatch of a modern destroyer, HMS Dauntless, to replace an older vessel, as well as Prince William, in his role as a search and rescue helicopter pilot, were provocations and presented a "grave risk for international security". Britain said the deployments were routine.

Argentina claims Britain stole the islands, situated 300 miles off the coast of Patagonia, in 1833. Argentina calls the archipelago Las Malvinas.

On Thursday, David Cameron reiterated British sovereignty, saying: "As long as the people of the Falkland Islands want to maintain that status, we will make sure they do and we will defend the Falkland Islands properly to make sure that's the case."

Tensions between the two countries have surged in the run-up to the 30th anniversary of the Falklands war.

Relations thawed in the 1990s but cooled again in 2010 when British firms started drilling for oil, triggering a diplomatic and commercial squeeze by Argentina's president. She recently convinced much of Latin America to ban ships flying the Falkland Islands flag from their ports.

The islands have since experienced shortages of fresh fruit, notably bananas, but otherwise claim to be unaffected. However, they fear Argentina will close its airspace to a weekly commercial flight between Chile and the islands, their main link to south America and the world.