Britain and Argentina on Monday marked 30 years since an Argentine invasion of the Falklands Islands triggered a bloody 74-day war, amid renewed tensions between the two countries. In Ushuaia, the world\'s southernmost city, some 5,000 people attended a remembrance vigil in honor of the 649 Argentines who died during the conflict. President Cristina Kirchner was expected to make a speech to veterans of the war and unveil a monument to the dead.  War veterans and Ushuaia residents braved zero degree Celsius temperatures to attend the vigil which began one minute after midnight. Later, Ushuaia Mayor Federico Sciurano inaugurated a cenotaph with the names of the 649 Argentines who perished during the war. The anniversary was to be marked across the country, including in Buenos Aires where leftist parties planned to stage a demonstration outside the British embassy.  In Britain, veterans of the conflict meanwhile gathered for a low-key service of remembrance, after Prime Minister David Cameron described the invasion of the South Atlantic islands as a \"profound wrong.\" The military junta that ruled Argentina stunned the world when it landed troops in the capital of the Falklands, Stanley, on April 2, 1982. The war ended in defeat for Argentina, costing the lives of 649 Argentine troops and 255 British servicemen, after Margaret Thatcher sent in a naval task force to reclaim the territory. Once the British troops had made the 8,000-mile (13,000-kilometer) sea voyage, they fought hilltop by hilltop until they wrested back control of the windswept islands Britain has ruled since 1833.  Argentina reasserted its claims of sovereignty over what it calls the Malvinas two years ago when Britain authorized oil companies to explore the waters around the archipelago. It has also accused Britain of militarizing the seas around the islands, taking its complaints to the United Nations. Amid heightening tensions, the British Ministry of Defense said on Monday that HMS Dauntless, a British destroyer, will head to the South Atlantic on Wednesday for a six-month patrol. The island\'s oil reserves, which remain untapped until now but which analysts say could be worth tens of billions of dollars, have been a major bone of contention between the two countries since their discovery in 1998.  At the United Nations in New York, the head of the Union of South American Nations (UNASUR) was to meet with UN chief Ban Ki-moon Monday to deliver a letter of support for Argentina in its row with Britain over the Falklands. The UN decolonization branch has called on London to open a dialogue on the islands, but Britain has refused. Cameron said Britain remains \"staunchly committed to upholding the right of the Falkland Islanders, and of the Falkland Islanders alone, to determine their own future.\"  \"Thirty years ago today the people of the Falkland Islands suffered an act of aggression that sought to rob them of their freedom and their way of life,\" he said. Britons were \"rightly proud of the role Britain played in righting a profound wrong,\" he added, paying tribute to the \"prosperous and secure\" society built there since the war. Falklands governor Nigel Haywood told AFP last week: \"The islands are British, we have full rights on the islands. The islanders themselves want to be British.\" At Britain\'s National Memorial Arboretum in central England, a candle was lit in memory of the veterans who lost their lives and will burn for 74 days to represent the duration of the conflict. Commander Peter Mosse, who captained a British naval frigate during the war, said after the service that the conflict was the product of the domestic situation in Argentina, which in 1982 was under the rule of a military junta. \"It was a very sad and unnecessary conflict because we were about to come to an arrangement with the Argentinians about the future of the Falklands by talking, by working things out, as things should be done,\" he told AFP. In a deliberately low-key service at the arboretum which lasted no more than 10 minutes, the congregation of fewer than 100 prayed for reconciliation between Britain and Argentina. A memorial to the 255 British servicemen who lost their lives is nearing completion in the arboretum grounds. It will be dedicated on May 20, in the presence of around 600 veterans. Reclaiming the islands became the defining moment of Thatcher\'s premiership and helped the \"Iron Lady\" to win re-election in 1983, and again in 1987. Thirty years on, London is facing a united Latin American front led by regional power Brazil over Argentina\'s territorial claims.