Britain refused Thursday to offer Libyan Foreign Minister Moussa Koussa immunity from prosecution

Britain refused Thursday to offer Libyan Foreign Minister Moussa Koussa immunity from prosecution after his apparent defection, but said his departure would hearten rebels fighting to topple Muammar Qaddafi’s regime.

British Foreign Secretary William Hague said the resignation of Koussa, one of the most senior members of Qaddafi’s government, shows that the Libyan leader’s regime is “fragmented, under pressure and crumbling.” But Hague said “Koussa is not being offered any immunity from British or international justice,” dampening speculation that the British government might seek to overlook allegations — leveled by Libya’s opposition — that he played a pivotal role in the 1988 bombing of Pan Am Flight 103, among other atrocities.

“Qaddafi must be thinking to himself, ‘Who will be the next to walk away’?” Hague said.

Hague said it wouldn’t be “helpful to advertise” whether or not other senior members of the regime planned to quit but that he believes many likely privately opposed Qaddafi’s actions.

Authorities debriefed Koussa, a trusted Qaddafi adviser and longtime stalwart in the Libyan regime, after he fled to Britain on Wednesday on a private plane from Tunisia — apparently with little notice to the British government.

Hague said Koussa was in a “secure place in the United Kingdom,” but did not disclose further details.