The Islamic State (ISIS) group advanced Sunday against rival rebel forces, including Islamists, in a bid to capture a series of key villages in northern Syria, a monitor said.
The Syrian Observatory for Human Rights said ISIS jihadists seized full control of Umm Housh, one of four villages in the northern province of Aleppo that lie along a rebel supply line from Turkey, which is a major backer of Syria's opposition.
"ISIS is trying to seize control of these villages from rebels to cut their supply route between Aleppo city and its outskirts, and the town of Azaz," a rebel bastion near the border, said Observatory head Rami Abdel Rahman.
He said two ISIS suicide bombers, one using a suicide belt and one in a bomb-laden car, began the assault on the villages on Saturday night.
The ensuing clashes, which continued throughout Sunday, left at least 37 rebel fighters and 10 ISIS jihadists dead, Abdel Rahman added. Another twenty rebels were reported missing in action.
ISIS has swept through territory in Iraq and Syria in an effort to build a cross-border "caliphate," and sees both the regime of Bashar al-Assad and rival rebel factions as its enemies.
And in recent months, the Assad regime has suffered major losses in Syria's north and east, as well as near its coastal heartland of Latakia province.
On Sunday, a powerful rebel coalition swept through additional villages in the Sahl al-Ghab plain, which borders the provinces of Latakia and Idlib, the Observatory said.
The Army of Conquest, which includes Al Qaeda affiliate Nusra Front, has edged closer to the regime's regional military headquarters in Jureen.
If the rebels manage to capture Jureen, they will be able to advance into the mountains of Latakia and bomb several communities from Assad's Alawite sect, an offshoot of Shi'ite Islam.
The Alawite bastion of Latakia city has seen tensions in recent days after a Syrian air force official was killed by Suleiman al-Assad, a cousin of the president, in an apparent road rage incident.
On Saturday, more than 1,000 people took to the streets in the city to protest the killing of Colonel Hassan al-Sheikh and to demand the execution of Suleiman al-Assad.
And on Sunday, Syria's official news agency SANA said the death toll from a rebel rocket attacks on the capital Damascus had risen to 11, including three children.
SANA said 46 people were also wounded, some critically, and that 10 of the dead were killed in the central Ath-Thawra neighborhood while the 11th person was killed in a nearby district.
The Britain-based Observatory, which uses a broad network of sources in Syria to gather information, confirmed the new toll.
AFP contributed to this report.