At least 29 people have been killed in fighting between Kurdish and jihadist fighters in northern Syria in the past two days, the Syrian Observatory for Human Rights said Thursday.
"At least 19 Al-Nusra Front (jihadist) fighters and 10 Kurds have been killed since the day before yesterday in clashes in the oil region of Hasakeh," the NGO said.
On Wednesday, the group said Syrian Kurdish fighters had pushed members of Al-Nusra and the Al-Qaeda-affiliated Islamic State of Iraq and the Levant out of the town of Ras al-Ain and its nearby border crossing with Turkey.
The clashes erupted after Al-Nusra Front militants attacked a convoy of Kurdish women fighters, Observatory director Rami Abdel Rahman said.
Activists in Ras al-Ain said members of the jihadist groups had taken advantage of the Muslim fasting month of Ramadan, which began last week, to try to impose their extreme version of Islam.
In the early days of the Syria conflict, when the opposition was desperate for help from any quarter, jihadists were welcomed but a spate of abuses has fuelled a major backlash.
The Observatory said jihadist fighters began firing rockets at Ras al-Ain, in western Hasakeh, after their expulsion.
They also attacked several roadblocks manned by Kurds and clashes were ongoing in the village of Tall Alu and Karhok in eastern Hasakeh, the group added.
Kurdish fighters, meanwhile, advanced elsewhere in the northeastern province, taking control of part of the Sweidiya area of Hasakeh, which is the only majority Kurdish province in Syria.
Syria's Kurdish minority has walked a sometimes ambiguous line in the conflict which is now in its third year.
Despite occasionally cooperating with rebels, Syria's Kurds have largely chosen to remain outside the conflict, seeking to exclude both regime troops and rebels from their areas.
The position has earned them the ire of some rebels, who fault them for failing to back the uprising.
The Kurdish community's more liberal interpretation of Islam has also made it a target for some extremist rebel groups, including Al-Nusra and the Islamic State of Iraq and the Levant.
Elsewhere on Thursday, the Observatory reported five killed in an air strike on the town of Saraqeb in northwestern Idlib province.
It said at least four missiles fired by regime warplanes hit residential buildings, killing five civilians and wounding dozens more including women and children.
In the central city of Homs, as regime forces press an offensive against rebel-held districts a rocket hit a school serving as a shelter for the displaced, the watchdog said.
There were conflicting accounts of the attack in the Dablan neighbourhood which the Observatory said killed four people.
The Syrian Revolution General Commission (SRGC) said it was an air raid, but the official SANA news agency said a mortar round fired by rebels killed three people.
In Damascus, the Observatory reported five soldiers killed when a booby-trap exploded as they entered a house in the Qaboon district during clashes.
It gave a provisional toll for violence on Thursday as 63 dead -- 22 soldiers, 26 rebels and 15 civilians.