Cairo - US Defence Secretary Leon Panetta said on Tuesday Nato operations in Libya will continue as long as there is heavy ground combat between rebels and diehard supporters of ousted strongman Muammar Gaddafi.
When asked how long Nato's air campaign would last, he said: "I think fighting has to end."
Nato operations were likely to carry on as "they can't continue to have the level of fighting that they have there," he told reporters during a visit to Cairo, where he met Egypt's military ruler Field Marshal Hussein Tantawi.
Nato air strikes began in March when Gaddafi's soldiers had rebels on the back foot, and helped tipped the balance in favour of the rebels who overran the capital Tripoli in August.
The poorly trained but now battle-hardened rebels have surrounded Gaddafi loyalists in Sirte, east of Tripoli, and Bani Walid southeast of the capital, with limited success so far in dislodging former regime fighters.
Nato planes struck targets in Sirte on Sunday, but Gaddafi loyalists were still in the fight, raining rockets and rocket-propelled grenades down on rebel positions the following day.
"Obviously there continues to be fighting by Sirte, by other areas" and "we still don't know where Gaddafi is," Panetta said.
"And so there still are some question marks with regards to the situation," he added at a news conference in Cairo.
Horror of the battle
But Panetta said the conflict "certainly is moving in the right direction" and "a lot of progress has been made" since the operation was launched in March.
The US defence chief will head to Brussels after Cairo to meet Nato defence ministers to discuss the allied air campaign in Libya, which was recently renewed for 90 days.
Hundreds of Sirte residents have been fleeing in packed vehicles, with some sitting on top of possessions piled high in the rear of pick-ups.
Civilians pouring out of Sirte said on Tuesday the horror of the battle for the city finally forced them to conquer their fear of the besieging new regime forces and leave.
The exodus comes as a commander of National Transitional Council (NTC) forces besieging the other remaining loyalist bastion of Bani Walid said Gaddafi's son Seif al-Islam was directing the last stand in the desert oasis.