BEIRUT -- With nearly 500 people reported killed in a week of rebel infighting, many Syrians barricaded themselves in their homes Friday, while others emerged from mosques angrily accusing an al-Qaida-linked group of hijacking their revolution.
The rebel-on-rebel clashes have overshadowed the battle against President Bashar Assad and underscore the perils for civilians caught in the crossfire of two parallel wars.
The violence, which pits fighters from a variety of Islamic groups and mainstream factions against the feared al-Qaida-linked Islamic State of Iraq and the Levant, have spread across four provinces in opposition-held parts of northern Syria.
The infighting is helping Assad, whose forces have clawed back some of the ground lost to the rebels in recent months as they bombard the north and other opposition regions with warplanes, heavy artillery and crude explosive-filled barrels dropped over rebel neighborhoods.
"The revolution has been derailed," said Abdullah Hasan, a self-described secular activist in the northern town of Maskaneh, where fighters from the al-Qaida-linked group swept in last month. "None of the groups fighting in Syria represent me now," he said, adding that he was nonetheless hopeful that the infighting would help purge extremists from the ranks of the rebels.
The latest bout of violence broke out a week ago across northern Syria and is the most serious among opponents of Assad since the civil war began.
The Britain-based Syrian Observatory for Human Rights said Friday that at least 482 people have been killed in the infighting since Jan. 3. It said 157 were from the Islamic State of Iraq and the Levant, 240 from more moderate factions and 85 were civilians.
The death toll exceeds casualties from the broader war between government forces and the rebels in the same time frame. The Observatory, which documents casualties on a daily basis through a network of activists on the ground, has recorded 385 people killed from Jan. 3 to Jan. 9 in fighting between rebels and government forces. But casualties among soldiers are difficult to track down and are often under reported.
The Islamic State of Iraq and the Levant and another al-Qaida-linked group known as Jabhat al-Nusra, or the Nusra Front, initially joined forces with moderate rebels fighting to oust Assad in a conflict that began in March 2011 as a popular uprising but morphed into a civil war.
The extremists proved well-organized and efficient fighters, giving the rebels a boost. But the Iraqi-based Islamic State of Iraq and the Levant, which includes many foreign fighters, has alienated many Syrians over the past several months by using brutal tactics to impose its strict interpretation of Islamic law.
The group has also kidnapped scores of foreign journalists and activists, and killed and beheaded opponents in areas it controls. This week, dozens of bodies were found at a hospital allegedly used as the group's local headquarters in Aleppo, many of them blindfolded and with their hands tied behind their backs.