"This is not a like a happy piece of news, is it?" Asked the spokesman. "But people are saying, 'So what?'  If someone who wants to step down, that's their decision. ... The fight continues. When I say the fight, I mean the struggle on all fronts."

Spokesman Moussa Ibrahim told reporters in Tripoli Thursday that Koussa had been granted medical leave to go to neighboring Tunisia. He added that the former foreign minister had not informed the government of his decision to "resign." 

Moussa then dismissed a question whether Koussa, who was intimately involved with the inner workings of the government of Moammar Gadhafi, now posed a threat.

"We do not think that he will sacrifice the safety and the future of his country. He is a man who truly - and seems maybe genuinely - feels tired and exhausted," Ibrahim said. "He is an old man. He has serious health problems. His heart, his body could not take the pressure.  We understand that."

Koussa, who is now in Britain, is the latest in a series of high profile Libyan officials to leave the Gadhafi government. At the beginning of the unrest last month, many diplomats overseas quit their posts, while at home, other ministers as well as military officers defected to the rebel ranks.

But Colonel Gadhafi is still surrounded by a cadre of loyalists, in particular his sons, two of whom are in charge of the nation's more powerful military forces.  

British and U.S. officials have left open what Koussa's future may be. They are walking a fine line in encouraging other Gadhafi loyalists to defect, while keeping in mind the call to prosecute Libyan officials implicated in alleged crimes of the Libyan government.