BEIRUT: Syrian rebel fighters freed at least 50 people Monday held captive by an Al-Qaeda-linked faction after clashes between the rival sides spread further in the country's opposition-held areas in the north, activists said.
The rebel-on-rebel fighting in Raqqa - a bastion of the Al-Qaeda-linked group known as the Islamic State in Iraq and the Levant - reflects a widening war within a war in Syria, this one against radical extremists.
It also suggests emboldened, recently formed rebel factions are trying to completely overrun their Al-Qaeda rivals in some areas of the north. The infighting has been the most serious since armed groups initially rose to try overthrow the rule of Syrian President Bashar Assad.
Tensions against Al-Qaeda-linked fighters had been simmering for months, with on-and-off clashes undermining the rebels' fight to topple Assad. Heavy fighting erupted in the northern provinces of Aleppo and Idlib again on Friday after residents there accused ISIL fighters of killing a popular doctor.
An activist group, the British-based Syrian Observatory for Human Rights, estimated that at least 100 fighters on both sides have been killed since Friday.
The rebels fighting against the ISIL are an unruly series of moderate and ultra-conservative groups who have little to unite them, except for their hatred of the Al-Qaeda group. The group is dominated by foreign fighters who initially fanned into Syria from neighboring Iraq in March and muscled into areas that rebels wrested from Assad-loyal forces, imposing their deeply conservative interpretation of Islamic law.
Rebels accused them of overtaking their areas, seizing their weapons and detaining their fighters. They also have eroded the good will of the locals by imprisoning Syrian civilians and detaining activists and journalists critical of their rule.
A coalition of Islamic brigades began clashing with ISIL forces in Raqqa overnight and the fighting continued Monday, said Rami Abdurrahman, the director of the Observatory. Another activist group, the Local Coordinating Committees, also reported the Raqqa clashes, saying they were focused around a city post office.
The Observatory said rebels surrounded the ISIL's chief compound in Raqqa and liberated at least 50 detainees from a nearby prison. Abdurrahman said they included fighters and activists imprisoned for their criticism of the ISIL.
The freed prisoners appeared to include fighters of an Islamic group, the Tawheed Brigade. In an online video, one of their freed bearded fighters is seen shouting, "This is Guantanamo!" The video corresponded with Associated Press reporting on the incident.
The Observatory said ISIL fighters retreated from the nearby town of Tal Abyad, along the Turkish border, after heavy fighting there. Clashes between the two sides continued in parts of Aleppo.
Raqqa was the first provincial capital to fall entirely into the hands of rebels, and was seized by the ISIL last year. An Italian Jesuit priest, Father Paolo Dall'Oglio, went missing in July after traveling to meet Al-Qaeda militants in Raqqa. Since then, rumors have swirled that foreign aid workers, reporters and Syrian activists have been held in Raqqa's detention centers.
Aburrahman estimated that more than 1,000 people being held in ISIL-run prisons in Raqqa province. He said the fate of the Italian priest and foreign journalists was unknown.
Activists said another Al-Qaeda-linked rebel group, the Nusra Front, was taking part in the fighting against ISIL in Raqqa, while in other places, the group was said to be trying to mediate a halt to the fighting.
Rebels of the more moderate Syrian Revolutionary Front - a recently formed coalition of rebel brigades aligned with the exiled Syrian opposition - appeared reluctant to give up their offensive.
In a statement Monday, they demanded ISIL fighters desert the Al-Qaeda group and join their ranks. They also accused the ISIL of killing at least 400 of their fighters and imprisoning 2,000.
"Were it not for these actions, the Front would not have raised its weapons," the statement said.
Rebels appear to have taken several ISIL compounds in the northern province of Aleppo. ISIL fighters also handed over strongholds in the town of Tal Rafat to the Nusra Front to avoid clashes, the Observatory reported.
Rebels and ISIL fighters fought in the town of Jarablous near the Syria-Turkey border. ISIL had seized key border crossings from the rebels over the past