The fighting raged as the West and some Arab regimes back more riots against President Bashar al-Assad’s government, which is preparing to participate in Geneva II peace talks.
A new front opened last Friday in Syria's nearly three-year-old war, when massive militant groups combined to attack bases and checkpoints of al-Qaeda linked Islamic State of Iraq and the Levant (ISIL).
"We have documented the killing of 482 people in the fighting -- 85 civilians, 240 members of the rebel brigades and 157 members of ISIL," said Syrian Observatory for Human Rights director Rami Abdel Rahman.
Among the civilians were 42 hostages who were brutally executed in Aleppo by ISIL foreign backed terrorists.
The militants also executed 47 ISIL terrorists, mainly in Idlib province in northwestern Syria, Abdel Rahman said.
"The rest of the deaths came during the fighting. It is likely dozens more civilians have lost their lives, but it is impossible to accurately document all the killings," he added.
The militant groups’ infighting has raged mainly in Aleppo, Idlib and Raqa provinces.
On Friday, militant groups continued to advance in much of Aleppo and Idlib, where ISIL's presence was relatively weak, while the ISIL terrorists had the upper hand in Raqa, which has been under their control for several months.
ISIL has its roots in Al-Qaeda in Iraq, and first appeared in the Syrian conflict in spring last year.
Civilians have suffered massively as a result of the latest infighting, activists say.
"In Aleppo city, people are trapped in their houses, unable to fetch medicine or food for fear they will get shot by snipers if they go outside," said a witness.
"In Raqa, the situation is even worse," he added.
ISIL has already carried out several deadly car bombings against civilians and rival militants in recent days, particularly in Aleppo and Idlib.
Protesters meanwhile took to the streets Friday, as they have every week since the start of the revolt in March 2011, this time chanting slogans against ISIL.
In the northern town of Binnish, protesters chanted: "Syria is free, free! ISIL, get out!"
NJF/NJF