BENGHAZI, Libya — Libyan rebel leaders said Sunday their forces hunted down and clashed with supporters of Moammar Gadhafi who had been posing as rebel fighters to infiltrate the opposition's eastern stronghold. The overnight battle killed four from each side and added to a sense of crisis within the rebel movement.

Libya's shaken rebels are trying to rid their ranks of enemies after the assassination last week of their military chief, Abdel-Fattah Younis. The leadership insists the slaying was the work of Gadhafi's regime, but several witnesses have said Younis was killed by fellow rebels.

As officials pieced together events leading up to Sunday's gunbattle, they announced that a faction of fighters called al-Nidaa was actually made up of Gadhafi loyalists posing as rebels. The revelation could raise questions about the loyalty of over rebel factions and sap the movement of much-needed unity in its push to topple Gadhafi nearly six months after the revolt began.

Suspicions about al-Nidaa were confirmed, a rebel security leader said, when intelligence officials determined the group was behind two prison break's on Friday in the rebels' de facto capital of Benghazi that freed 200 to 300 inmates, including pro-Gadhafi mercenaries, fighters and other regime loyalists.

"These people took advantage of the chaos that resulted from the killing of Younis and entered and attacked the military prison and the (civilian) Kuwaitiya prison," said the rebel's deputy interior ministry, Mustafa al-Sagezli.

On Sunday before dawn, rebel forces tracked al-Nidaa members to a factory where they were hiding out and sent in negotiators to try to persuade them to surrender. When they refused, the rebel units besieged the factory, killing four of the Gadhafi fighters, said rebel Information Minister Mahmoud Shammam.

A battlefield commander who participated in the operation, Ismail Salabi, said four of those posing as rebels were also killed and 25 were captured. He described them as Libyans from the southern part of the country who belonged to the Gadhafi Brigades.

"This is a hard hit for the fifth column," he said.

Rebel forces also seized 40 of the freed prisoners, who were found hiding out with the fighters.

Talk of a fifth column adds to the disarray that was set off with Thursday's killing of the chief rebel commander, Younis, in still mysterious circumstances. The leadership says authorities had arrested him on suspicion of mismanaging forces under his command and that gunmen attacked while he was being transported from one location to another under heavy guard.

Several rebels who witnessed the attack, however, said he was killed by his own side. Younis was Gadhafi's interior minister before defecting to join the rebels.

In the Nafusa mountains of western Libya near the Tunisian border, rebel forces said they were making gains in their push against Gadhafi forces from the other main front line.

On Sunday, they said they were in the town of Hawamid and advanced another six to nine miles (10-15 kilometers) toward the small town of Tiji in the last 24 hours.

"Hundreds of rebel fighter are surrounding Tiji," said Jamal Motawa, a 26-year-old rebel who was one of seven wounded in the fighting. Motawa had shrapnel in his left leg.

Pro-Gadhafi forces inside Tiji were under siege but continued to attack the advancing rebels with rockets, according to Motawa.

Tiji is on the main road from the Tunisian border to Tripoli, the Libyan capital. It is considered a strategically important town if rebels were to continue their advance to Tripoli, some 150 miles (240 kilometers) to the northeast.

Rebels in the Nafusa mountains have been making modest advances against Gadhafi's troops, but fighting in the east has been stalled for months, with neither side able to make any significant progress.

Despite the slow pace of events on the ground, France, one of the rebels' main outside backers, is counseling patience.

In an interview published on Sunday, French Defense Minister Gerard Longuet addressed the growing pressure for a quick resolution to the Libya conflict, insisting that "impatience is never a good adviser" and that rebel fighters don't deserve the blame.

"Things have to move in Tripoli. To put it clearly, the population has to rise up. The month ahead will naturally be intense. There will not be, I think, a pause because of the month of Ramadan," Longuet said.

On Sunday, a day after NATO airstrikes hit three Libyan state television satellite transmitters in Tripoli, a spokesman at NATO's operational headquarters in Naples said the alliance had seen reports of casualties among the TV network's employees.

"We are aware of the allegations related to this subject," said a NATO official who could not to be identified in line with standing restrictions. "We cannot confirm them since we have nobody on the ground there."

He noted that the Libyan government had on several past occasions claimed that NATO airstrikes had killed civilians, but that most of these proved to be false.

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On Saturday, the head of Libyan state TV's English-language section told reporters in Tripoli that three state television journalists were killed and 15 other people were wounded in the NATO strikes.

"We are not a military target. We are not commanders in the army and we do not pose a threat to civilians," Khaled Bazelya said.

NATO said the strike was launched because Gadhafi was using Libyan TV to "incite acts of violence."

Associated Press writers Karin Laub in Nalut, Libya, Slobodan Lekic in Brussels and Jamey Keaten in Paris contributed to this report.