BRUSSELS (AP) — There is no clear set of conditions in Libya that will trigger an end to the combat mission, but the operation will not be over if serious fighting and threats to the population continue, Defense Secretary Leon Panetta said Thursday.

Speaking to reporters at a meeting of NATO defense ministers in Brussels, Panetta said the ministers agree that the decision will depend on whether forces loyal to ousted leader Moammar Gadhafi are still able to attack civilians and whether the opposition forces are able to provide security for the country as it moves to democracy.

His comments made clear that there is no definitive end to the mission, and did not rule out additional extensions to the operation, which is set to end in late December.

At the same time, NATO ministers spoke optimistically about the Libya operation, suggesting it is close to over.

NATO Secretary-General Anders Fogh Rasmussen asserted that “It is clear that the end is in sight. Qadhafi’s forces are fighting for a lost cause. The threat to civilians is fading away. The recent positive developments in Libya are irreversible.”

Both he and Panetta, however, said that if serious threats to the population continue, the mission will go on.