London: Britain's "special relationship" with the US could come under stress as Washington throws its support behind the Argentine foreign minister's bid to become the next UN Secretary-General. The White House is reportedly enthusiastic in its backing of Susana Malcorra's application for the UN's top job, despite the concerns of its "closest ally" Britain. The US move could be interpreted as a snub, threatening to expose existing differences in policy between Britain and America over the Falkland Islands, known to Argentina as Las Islas Malvinas. While Britain backs the islanders' right to self-determination, the US holds on tightly to its historic policy of conspicuous silence over the issue. A 2013 referendum on the Falkland Islands -- over which Britain went into war with Argentina in 1982 after Argentina seized them -- found 99.8 percent of the population favours remaining part of Britain. "It's a really tough call for the UK. There is obvious concern at having someone heading up the UN who firmly believes that the Falklands should belong to Argentina," a British diplomat was quoted as saying by the Daily Mail. "But at the same time, Downing Street doesn't want to appear petty by blocking an otherwise excellent candidate, just for her country's claim." Since becoming Argentina's foreign minister last December, Malcorra has insisted the Falklands question is no longer a major issue, as it had been with the previous government. However, she said the Malvinas -- as the Falklands are referred to in Argentine -- are still "a top priority because they are in the constitution and if I were to dismiss the issue. I would be going against the constitution." Washington refused to take sides during the Falklands War, to the grievance of the British government at the time, and has refused to go public on the issue since then.