Jihadists from the Islamic State of Iraq and the Levant (ISIS) executed at least 22 people, including 12 rebels, in the north of the country on Tuesday, a monitoring group told the AFP news agency.
"ISIS members executed at least 22 persons with firearms or knives, after taking control of Shuyukh outside the town of Jarabulus" in Aleppo province, Rami Abdel Rahman, head of the Syrian Observatory for Human Rights, said.
Among those killed were "at least 12 armed rebels," he added.
The jihadist ISIS seized Jarabulus, near the northern border with Turkey, from the rebels last month.
Since it joined the civil war in Syria, ISIS has been accused of several human rights abuses, including torturing and murdering prisoners, among them children and teenagers, and forcing Druze men to convert to Islam or die.
SIS has been targeted by rival rebel groups. In recent weeks, three powerful rebel alliances – among them Islamist groups - have teamed up to fight ISIS, which they have warned is even worse than Bashar Al-Assad’s regime.
At least 3,300 persons have been killed in that fighting, according to the Britain-based Observatory, which relies on activists and other sources inside Syria.
Even the central leadership of Al-Qaeda has renounced ties with ISIS, though that decision was probably a political one and not because of the group’s actions.
ISIS leader Abu Bakr al-Baghdadi has repeatedly ignored calls from Al-Qaeda chief Ayman al-Zawahiri for an end to infighting between his group and the Al-Nusra Front, Al-Qaeda's official satellite organization in Syria.