Fierce fighting between jihadists and rival opposition groups in Syria in the past nine days has killed at least 700 and led to the disappearance of hundreds more.
Since early January, opposition groups have been battling the jihadist Islamic State of Iraq and the Levant, which is accused of abuses against other militants, activists and civilians in areas where they operate.
Opposition Observatory said "from January 3 to 11, the fighting killed 697 people, among them 351 rebel fighters, 246 members of the Islamic State of Iraq and the Levant and 100 civilians", adding dozens more deaths have yet to be documented.
The Observatory said there were "hundreds of captives from both sides whose fate is unknown".
In a reflection of the brutality of the fighting, which has raged mainly in the northern provinces of Aleppo, Idlib and Raqa but has also hit Hama and Homs, at least 200 people were killed in one 48-hour period.