AJDABIYA, Libya — Troops loyal to Moammar Gadhafi knocked back rebels for a third straight day Thursday but there were signs that the embattled regime is cracking at the highest levels: the defection of the second top official in roughly 48 hours.
Ali Abdessalam Treki, a former foreign minister and U.N. General Assembly president, had been named to represent Libya at the United Nations after a wave of defections early in the uprising. But Treki, who is currently in Cairo, said in a statement posted on several opposition websites that he was not going to accept that job or any other.
"We should not let our country fall into an unknown fate," he said. "It is our nation's right to live in freedom, democracy and a good life."
In addition, Al Jazeera television said that "a number of figures" close to Gadhafi had left Libya for Tunis, a day after Foreign Minister Moussa Koussa defected.
Citing unnamed sources, Al Jazeera said the group included the chairman of Libya's National Oil Corporation Shokri Ghanem. But earlier Thursday, Ghanem said by phone that he was in Libya: "I am in Tripoli and I am in my office."
Also named by Al Jazeera were the speaker of Libya's General People's Congress Mohamed Abdul Qasim al-Zwai, foreign intelligence chief Abuzeid Dorda and Abdelati al-Obaidi, a senior diplomat in charge of European affairs.
On Wednesday, Koussa flew to England from Tunisia and the British government said he had resigned. He is privy to all the inner workings of the regime, so his departure could open the door for some hard intelligence, though Britain refused to offer him immunity from prosecution.
"We believe that the regime is crumbling from within," opposition spokesman Mustafa Gheriani said in Benghazi, the rebels' de facto capital.
Gadhafi issued a defiant statement after the departures, calling on the leaders of countries attacking his forces to resign and accusing them of being "affected by power madness."
"The solution for this problem is that they resign immediately and their peoples find alternatives to them," the Libya state news agency quoted him as saying.
Gheriani compared the Libyan strongman to a wounded animal.
"An injured wolf is much more dangerous than a healthy wolf. But we hope the defections continue and I think he'll find himself with no one around him," Gheriani said.
Libyan officials, who initially denied Koussa's defection, said he had resigned because he was sick with diabetes and high blood pressure.
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Nations behind the campaign of international airstrikes that have hobbled Libya's military hailed Koussa's resignation as a sign of weakness in Gadhafi's more-than-41-year reign.
Koussa "can help provide critical intelligence about Gadhafi's current state of mind and military plans," said Tommy Vietor, U.S. National Security Council spokesman. He added that his defection "demonstrates that the people around Gaddafi understand his regime is in disarray."
U.N. Secretary-General Ban Ki-moon's special envoy, Abdelilah Al-Khatib, arrived Thursday in Tripoli, U.N. spokesman Farhan Haq said. He was also expected to talk to the Libyan opposition, Haq said, without providing details.
In another blow to the regime, U.S. officials revealed Wednesday that the CIA has sent small teams of operatives into rebel-held eastern Libya while the White House debates whether to arm the opposition.
Despite the setbacks and ongoing airstrikes — now led by NATO — Gadhafi loyalists have retaken much of the territory the rebels had captured since airstrikes began March 19.
Rebels had advanced overnight to the west gate of Brega, a town important to Libya's oil industry that has gone back and forth between rebel and loyalist hands. They were in Brega at dawn, but they soon pulled out under heavy shelling from Gadhafi's forces. Black smoke billowed in the air over Brega as mortars exploded.
"There were loads of (rebel) wounded at the front lines this morning," said rebel fighter Fathi Muktar, 41.
Rebels fired back from sand dunes, chanting "Allahu akbar!" or "God is great!" with each rocket fired. Spotters with binoculars watched where they landed and ordered adjustments.
Brega was deserted and Jabbar Ali, 25, a rebel aviation technician, said Gadhafi's forces were at its eastern gates and controlled much of the city.
Many people also have fled Ajdabiya, a rebel-held city about 50 miles (80 kilometers) to the east, for fear that government forces were on their way.
The fighting has highlighted the rebels' weaknesses: Some ran screaming to cars after being frightened by the outgoing fire from their own side.
The U.S. has ruled out using ground troops in Libya but it is considering providing arms to the rebels. Still, White House press secretary Jay Carney said Wednesday no decision has been made yet.
Defense Secretary Robert Gates, however, told Congress on Thursday that the U.S. still knows little about the rebels, and that if anyone arms and trains them it should be some other country.
Asked by a lawmaker whether U.S. involvement might inevitably mean "boots on the ground" in Libya, Gates replied, "Not as long as I am in this job."
NATO is among those saying a new U.N. resolution would be required to arm rebels, though Britain and the U.S. disagree. Several world leaders oppose arming rebels, including Turkish Prime Minister Recep Tayyip Erdogan who said in London that it could "create an environment which could be conducive to terrorism."
NATO has warned the rebels not to attack civilians as they push against Gadhafi troops, or they, too, could get bombed, The New York Times reported.
“We’ve been conveying a message to the rebels that we will be compelled to defend civilians, whether pro-Gadhafi or pro-opposition,” a senior Obama administration official to the Times. “We are working very hard behind the scenes with the rebels so we don’t confront a situation where we face a decision to strike the rebels to defend civilians.”
Koussa is not the first high-ranking member of the regime to quit — the justice and interior ministers resigned early in the conflict and joined the rebellion based in the east. Koussa, however, is a close confidant of Gadhafi's.
Koussa was Libya's chief of intelligence for more than a decade. The opposition blames him for the assassinations of dissidents in western capitals and for orchestrating the 1988 Lockerbie bombing over Scotland and the bombing of another jet over Niger a year later. The links have never been confirmed.
In later years, however, Koussa played an important role in persuading Western nations to lift sanctions on Libya and remove its name from the list of state sponsors of terrorism. He led settlements of Lockerbie, offered all information about Libya's nuclear program and gave London and Washington information about Islamic militants after the Sept. 11 attacks.
Scottish prosecutors say they've asked Britain's Foreign office to speak with Koussa about the Lockerbie bombing, which killed 270 people.
Abdel Basset al-Megrahi, a former Libyan agent, was sentenced to life in prison in 2001 for his part in blowing up the airliner but was released by the Scottish government in 2009 when he was judged by doctors to be terminally ill.
Koussa played a key role in the release of al-Megrahi.
British Foreign Secretary William Hague said Koussa would not be given immunity from prosecution. However, there are concerns that deals could be struck with Koussa in return for providing useful information about Gadhafi.
Prime Minister David Cameron said police and prosecutors would be free to pursue any evidence.
Reuters and The Associated Press contributed to this report.