Before the convoy had traveled two miles, NATO officials said, it was set upon by an American Predator drone and a French warplane. With the attack the convoy “was stopped from progressing as it sought to flee Surt but was not destroyed,” Defense Minister Gérard Longuet of France said.

Only two vehicles in the convoy were hit, neither carrying Colonel Qaddafi, a Western official said. But the rest of the convoy was forced to detour and scatter. Anti-Qaddafi fighters rapidly descended on the scene, telling Reuters they saw people fleeing through some nearby woods and gave pursuit.

A field leader in Surt, who gave his name to Al Jazeera television as Mohammed al-Laith, said that Colonel Qaddafi fled from a Jeep in the convoy and dived into a large drainage pipe. After a gun battle backed by his guards, he emerged. Mr. Laith told Al Jazeera that the former Libyan leader had a Kalashnikov in one hand, a pistol in the other.

Image Surt was Colonel Qaddafi’s hometown and final redoubt in the eight-month conflict. Credit... The New York Times

“What’s happening?” he quoted him as asking as he came out.

The video on Al Jazeera shows Colonel Qaddafi wounded, but clearly alive. The network quoted a fighter saying that he had begged for help. “Show me mercy!” he was said to have cried. There was little of that, in the video at least.

One fighter is seen pulling his hair, and others beat his limp body. Two fighters interviewed by Al Jazeera said someone had struck his head with a gun butt.

Omran Shaaban, 21, a Misurata fighter who claimed to have been the first, along with a friend, to find Colonel Qaddafi, said he was already wounded in the head and chest and bleeding in the drainage pipe and then whisked away to an ambulance. Precisely how he died after that, Mr. Shaaban said, was unclear.