Libyan Foreign Minister Moussa Koussa arrived in Britain on Wednesday and has resigned from Muammar Gaddafi's government, the British government said.
"We can confirm that Moussa Koussa arrived at Farnborough Airport on 30 March from Tunisia. He travelled here under his own free will. He has told us he is resigning his post," a Foreign Office spokesman said in a statement.
"Koussa is one of the most senior figures in Gaddafi's government and his role was to represent the regime internationally -- something that he is no longer willing to do," the spokesman said.
The British government encouraged people around Gaddafi to abandon him, he added.
Meanwhile, US President Barack Obama signed a secret order authorizing covert US government support for rebel forces seeking to oust Gaddafi, government officials told Reuters on Wednesday.
Obama signed the order, known as a presidential "finding", within the last two or three weeks, according to four US government sources familiar with the matter.
Such findings are a principal form of presidential directive used to authorize secret operations by the Central Intelligence Agency. The CIA and the White House declined immediate comment.
News that Obama had given the authorization surfaced as the President and other US and allied officials spoke openly about the possibility of sending arms supplies to Gaddafi's opponents, who are fighting better-equipped government forces.
The United States is part of a coalition, with NATO members and some Arab states, which is conducting air strikes on Libyan government forces under a UN mandate aimed at protecting civilians opposing Gaddafi.
In interviews with American TV networks on Tuesday, Obama said the objective was for Gaddafi to "ultimately step down" from power. He spoke of applying "steady pressure, not only militarily but also through these other means" to force Gaddafi out.
Obama said the US had not ruled out providing military hardware to rebels. "It's fair to say that if we wanted to get weapons into Libya, we probably could. We're looking at all our options at this point," the President told ABC News anchor Diane Sawyer.
US officials monitoring events in Libya say that at present, neither Gaddafi's forces nor the rebels, who have asked the West for heavy weapons, appear able to make decisive gains.
While US and allied airstrikes have seriously damaged Gaddafi's military forces and disrupted his chain of command, officials say, rebel forces remain disorganized and unable to take full advantage of western military support.
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