The defection of Libya’s foreign minister, a member of Moammar Gadhafi’s inner circle, is the latest sign that the embattled regime is cracking at the highest levels as the West keeps up pressure on the longtime leader to relinquish power.

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 NATO airstrikes on government forces, Gadhafi loyalists have been logging successes on the battlefield, retaking much of the territory the rebels had captured since airstrikes began March 19.

Britain’s government said Wednesday that Foreign Minister Moussa Koussa had arrived in Britain on a flight from Tunisia and was resigning from his post, though the Libyan government denied it. British Foreign Secretary William Hague said the resignation showed the regime is “fragmented, under pressure and crumbling.”

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, privy to all the inner workings of the regime. His departure could open the door for some hard intelligence, though Britain refused to offer him immunity from prosecution.

Koussa was Libya’s chief of intelligence for more than a decade. The opposition holds responsible for the assassinations of dissidents in western capitals and for orchestrating the 1988 Lockerbie bombing and the bombing of another jet over Niger a year later.

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.

“His defection is a serious blow” to Gadhafi, Elliott Abrams, a former assistant secretary of state under President Ronald Reagan, said in a story posted on the Council on Foreign Relations’ website. “This is the first loss of such a close comrade,” he said, adding that he may have be able to identify other potential defectors.

Abrams, who met Koussa in 2004 in negotations over Libya’s handover of weapons of mass destruction programs, described him as a handsome, well-dressed man speaking perfect English. Koussa attended Michigan State University in the 1970s.

Abrams said the simple fact that Koussa was able to make it to England “suggests that the regime is falling apart despite its battlefield victories in the last two days.” His departure suggest that Gadhafi’s inner circle “now know how this story ends, and do not wish to be with the dictator when that end comes,” he said.

On Thursday, the rebels came under heavy shelling by Gadhafi’s forces in the strategic oil town of Brega on the coastal road that leads to Tripoli. Black smoke billowed in the air over Brega as mortars exploded.

“Gadhafi’s forces advanced to about 30 kilometers east of Brega,” said rebel fighter Fathi Muktar, 41. Overnight, he said the rebels had temporarily pushed them back, but by morning they were at the gates of Brega. “There were loads of wounded at the front lines this morning,” he said of rebel casualties.

The poorly equipped rebels’ setbacks are hardening the U.S. view that they are probably incapable of prevailing without decisive Western intervention, a senior U.S. intelligence official told The Associated Press.

The U.S. has made clear that it is considering providing arms to the rebels. Still, White House press secretary Jay Carney said Wednesday no decision has been made yet.

“We’re not ruling it out or ruling it in,” he said.

Obama said in a national address Monday night that U.S. troops would not be used on the ground in Libya.