Rebels battled pro-Moammar Gadhafi forces Thursday in Libya's east and faced stubborn resistance in the capital while the opposition moved to assert control over the oil-rich country even as the longtime dictator remained at large.

The rebels have seized control of much of Tripoli as Gadhafi's 42-year regime crumbled, but the autocrat has refused to surrender and has vowed from hiding to fight on "until victory or martyrdom."

The rebel leadership has offered a $2 million bounty on Gadhafi's head, and British Defense Secretary Liam Fox said Thursday that NATO was helping in the search for the longtime dictator.

Fox told BBC Radio 4 that NATO was "providing intelligence and reconnaissance assets to help in the hunt," and had been heavily active in carrying out overnight airstrikes against Gadhafi loyalists, but refused to say if British special forces were involved.

Rebels say one of their key targets now is Gadhafi's hometown of Sirte, about 250 miles (400 kilometers) from Tripoli, but acknowledged that capturing that city would not be easy because Gadhafi's fellow tribesmen were expected to put up a fierce fight. Opposition leaders have said they were trying to negotiate a peaceful surrender of the city.

Fawzi Abu Ketf, deputy defense minister of the rebel National Transitional Council, said fighting was raging Thursday outside Bin Jawad, 400 miles (650 kilometers) south of Tripoli, but he had no details. Gadhafi loyalists ambushed rebels advancing toward the city on Wednesday, killing at least 20 of them.