Fierce fighting between jihadists and rival rebel groups in Syria in the past nine days has killed at least 700 and led to the disappearance of hundreds more, an NGO said Sunday.

"From January 3 to 11, the fighting killed 697 people, among them 351 rebel fighters, 246 members of the (jihadist) Islamic State of Iraq and the Levant and 100 civilians," said the Syrian Observatory for Human Rights, adding that dozens more deaths have yet to be documented.