BENGHAZI, Libya – Rebels battled Moammar Gadhafi’s forces on a deadlocked front line in eastern Libya, and NATO warplanes struck Tripoli early today in the heaviest bombing of the Libyan capital in weeks.

Overnight, NATO warplanes struck at least four sites in Tripoli, setting off crackling explosions that thundered through the Libyan capital.

One strike hit a building that local residents said was used by a military intelligence agency. Another targeted a government building that officials said was sometimes used by parliament members.

It was not immediately clear what the other two strikes hit, but one of them sent plumes of smoke over the city. Libyan officials would not say what that strike hit but the smoke appeared to come from the compound housing members of Gadhafi’s family.

On the front line, heavy fighting was reported Monday south of Ajdabiya, a rebel-held town about 90 miles south of Benghazi, the rebel headquarters in the east.

Hundreds of rebels gathered at a checkpoint outside Ajdabiya on Monday afternoon, when an Associated Press photographer counted about 100 pickup trucks coming back from the front, each carrying four or five fighters and some with mounted submachine guns.

The rebels, firing their weapons into the air as they shouted and danced, said they had been told that NATO was going to launch airstrikes on Gadhafi’s forces and they had been ordered to withdraw temporarily from the front.