Libyan rebels staged an armed uprising against Moammar Gaddafi in the western city of Zlitan on Friday, a rebel spokesman said, adding that 22 of their fighters had been killed.

The clashes, if confirmed, would mark the first significant rebel attempt to take control of a major city in western Libya since the early days of the uprising.

Zlitan lies just over 100 miles east of Tripoli and about 30 miles west of the besieged rebel-held city of Misurata. A Libyan government spokesman could not be reached for comment and there was no independent confirmation of the rebel claims.

“There is a battle around the main hospital in Zlitan as we speak,” said Mohamed Ali, a rebel spokesman from Misurata currently in the Qatari capital, Doha.

Meanwhile, Gaddafi’s forces stepped up their assault on Misurata, pounding rebel positions to the west of the city with tanks and rocket fire Friday, killing at least 31 people, rebels said.

“This is one of the bloodiest days ever in Misurata, and NATO is nowhere to be seen,” Ali said. “Where are they?”

The shelling near Misurata came as Defense Secretary Robert M. Gates issued a stinging rebuke of some of America’s staunchest allies, complaining that European budget cuts and reluctance to fight have made missions in Libya and Afghanistan significantly more difficult and shifted the burden onto the United States.

Ali said Gaddafi’s son Khamis had taken charge of the renewed attack on Misurata, which had killed 96 people in the past week, most of them rebel fighters. He said 85 people had been wounded Friday.

“One of the soldiers we captured said Khamis has told his troops, ‘Take Misurata or I will kill you myself. If you don’t take Misurata, we are finished.’ ”

Misurata was subjected to daily shelling by government forces in March and April, but rebels eventually forced Gaddafi’s troops out of the city after intense clashes, and there had been a lull in the fighting for the past few weeks.

In Ankara, Turkish Prime Minister Recep Tayyip Erdogan said Friday that his country had offered a “guarantee” to Gaddafi if he left Libya but that it had received no answer.

“Gaddafi has no way out but to leave Libya, through the guarantees given to him, it seems,” Erdogan told NTV television in an interview, the Reuters news agency reported.

“We ourselves have offered him this guarantee, via the representatives we’ve sent. We told him we would help him to be sent wherever he wanted to be sent. We would discuss the issue with our allies, according to the response we receive. Unfortunately, we still haven’t got a response from Gaddafi.”

Erdogan, whose country is a member of NATO, did not specify what kind of guarantee his country had offered.