Syria crisis: Rebel groups 'execute rivals'
Thirty-four foreign jihadists have been singled out by rival Syrian rebels and killed, say UK-based activists.
It happened over the past three days in Jabal al-Zawiya, north-western Idlib province, said the Syrian Observatory for Human Rights.
Meanwhile, activists in Aleppo city told the BBC militants from one of the same jihadi groups, ISIS, had summarily executed at least 50 captives.
A regional battle is pitting ISIS against an alliance of rival rebels.
A coalition of moderates and other Islamists fighting to depose President Bashar al-Assad is ranged against ISIS in several parts of northern Syria.
The al-Qaeda-linked ISIS - Islamic State in Iraq and the Levant - is accused by other rebel groups of undermining the struggle against the regime of President Assad, focusing on accumulating territory and imposing a rule of terror in the areas it controls.
The fighting is continuing in Raqqa, a city under full rebel control and previously an ISIS stronghold.
Separately, the Observatory says the death toll from a government air campaign launched in Aleppo province in mid-December now exceeds 600, including 225 children and women.
On its Facebook page, it pledged to "work tirelessly" for the prosecution of those responsible for the massacres in the International Criminal Court.
Most of the 34 reported dead in Jabal al-Zawiya were ISIS fighters, with the remainder from a smaller allied group called Jund al-Aqsa, the Observatory said.
The execution of the "non-Syrian" fighters had been confirmed by medical and local sources, it said.
Those executed by ISIS in Aleppo were said to include medics, local journalists and members of rival rebel groups.
None of the reported killings can be independently confirmed.
The reported killing of prisoners held by ISIS could undermine initiatives by radical clerics to reconcile the warring Islamist factions in northern Syria, says BBC Arabic correspondent Ahmed Maher.
Since last Thursday, large-scale attacks by an alliance of moderate Islamist factions and rebel groups have been taking place across northern and north-eastern Syria on ISIS strongholds and strategic positions, inflicting heavy losses on ISIS. Scores are said to have died, including civilians.
The alliance says that the offensive is driven by public anger in ISIS-controlled territories over practices including strict interpretation of Islamic laws as well as the kidnapping of journalists and horrific torture of prisoners, our correspondent explains.
Experts in Islamist movements, however, place the conflict in the context of a power struggle between all Islamist factions.