Moderate rebels clashed with Al-Qaeda affiliate the Nusra Front in Idleb province of northwest Syria on Friday, a monitoring group said.
The clashes, near a Syrian Revolutionary Front bastion in Deir Sinbel village, came days after the Nusra Front took over checkpoints, according to the Syrian Observatory for Human Rights.
"Both sides suffered heavy losses," said the Britain-based group.
A Zaman al-Wasl reporter said the chief of the Syrian Revolutionary Front, Jamal Maarouf, has withdrawn with his fighters from their stronghold in Deir Sunbul, accusing other rebel groups in the Free Syrian Army of abandoning them with no military support.
On Thursday, another clash pitted the moderate Hazm movement against the Nusra Front in Khan al-Subul, also in Idleb, killing three fighters.
Both the Hazm Brigade and the Syrian Revolutionary Front have relations with the West and want the establishment of a democratic state in Syria.They are also fiercely critical of jihadist groups.
Activists published a video showing Maarouf, dressed in military gear and walking among fighters.
He addresses the Nusra leader Abu Mohammad al-Jolani, saying: "You have tarnished the name of Islam, and you have tarnished religion. Why do you fight us? Go away, fight the regime!"
"You are nothing; you are just like Baghdadi… you bastard," he added.
Maarouf was referring to Abu Bakr al-Baghdadi, who heads the Islamic State of Iraq and Syria (ISIS) group, known for its horrific atrocities.
Nusra hit back on Twitter, accusing Maarouf of "corruption" and of "straying from the path of the revolution".
Idleb province was among the first areas to fall from government control, soon after the outbreak of a revolt against President Bashar al-Assad's regime in 2011.
Meanwhile, 150 Iraqi peshmerga fighters, who arrived Thursday on the Turkish side of the border, were still waiting to cross and join fellow Kurds defending the town of Kobani, or Ayn al-Arab.
The Observatory said Syrian Kurdish fighters advanced on an ISIS post in the north of the town, leaving many dead among the jihadists.
In the center of town, ISIS blew up a car bomb near Kurdish positions, it said.
The Observatory also reported that artillery pieces were destroyed and ISIS fighters killed as U.S.-led coalition air strikes targeted the north and centre of Kobani.
Translated and edited by The Syrian Observer