A senior Republican criticised the Obama Administration yesterday for its failure to back Britain in its dispute with Argentina over the Falkland Islands, citing the support that the UK received from President Reagan in the 1982 conflict.

“The US must stand with the UK on this issue as we did in the 1980s,” said Mac Thornberry, who served on the Armed Services and Intelligence committees in the House of Representatives. “There should be no doubt where the US should stand,” he added, referring to Britain’s role as America’s closest ally. “The level of co-operation between our two countries is certainly more important than any one issue.”

Referring to a meeting between Hillary Clinton and President Fernández de Kirchner of Argentina this week, when the US Secretary of State angered London by offering to “mediate” in the dispute, Mr Thornberry added: “I am hoping that behind the scenes, she was telling the Argentinians to back down.”

The meeting was viewed with particular concern in Whitehall because it was seen in Argentina as a diplomatic victory in its attempts to force Britain into talks. Despite it being made clear to the State Department that the UK was not interested in discussions regarding the islands’ sovereignty, Mrs Clinton, in response to a request from Mrs Kirchner for a “friendly mediation”, said that talks were a sensible way forward “to encourage both countries to sit down”.

The row has been reignited by the UK’s plans to drill for oil around the islands. The UK has ruled out any concessions, insisting that there was “no question” over Falklands sovereignty or any need for mediation by a third party as long as the residents wanted to remain British.

The fear in London is that, without clear backing from the US, Britain might be undermined because Latin America is rallying behind Argentina — a position that the Obama Administration appears loath to contradict.

Back in 1982 Washington’s backing over the Falklands conflict was not immediately forthcoming because the US initially tried to remain neutral. Only after Casper Weinberger, the US Defence Secretary, insisted to Mr Reagan that neutrality was not an option did the White House voice support for Margaret Thatcher’s decision to retake the islands from the Buenos Aires military regime.