At least 20 Druze villagers have been shot dead by the al-Qaeda-affiliated al-Nusra Front in north-western Syria, activist and opposition groups say.
The Syrian Observatory for Human Rights said elderly people and a child were among those killed in Qalb Lawzah in Idlib province on Wednesday afternoon.
The Druze faith is an offshoot of Islam considered heretical by jihadists.
However, al-Nusra's leader vowed last month not to harm members of religious minorities who did not fight it.
The group is part of a rebel alliance, the Army of Conquest, which has taken control of much of Idlib in the past three months, driving out government forces.
Another rebel alliance was reported to have launched an assault on the government air base in the south of the country on Thursday.
A rebel spokesman said they had managed to seize most of the al-Thala base, but state television reported that three rebel attacks had been repelled.
The Syrian Observatory, a UK-based monitoring group, reported that Wednesday's shooting occurred after a Tunisian al-Nusra commander tried to confiscate a house belonging to a Druze man who he claimed was loyal to the Syrian government.
Relatives of the house's owner protested and tried to stop the commander.
The dispute soon turned violent and a villager was shot dead before another seized the rifle of an al-Nusra fighter and opened fire, killing one of the jihadists, the Syrian Observatory said. Reinforcements were called in by the commander and at least 20 villagers were shot, it added.
Sources told the BBC that the al-Nusra commander accused the Druze of being "kuffar" (infidels) before ordering the mass shooting, and that rebel groups allied to al-Nusra, including Ahrar al-Sham, eventually intervened to stop the bloodshed.
The main Western-backed opposition alliance, the National Coalition, said an armed clash broke out "following an aggression by al-Nusra Front members" and that it had left "dozens of Druze men" dead.
The Druze made up about 3% of Syria's 22.5 million population before the uprising against President Bashar al-Assad began in 2011.
Many Druze live in the Jabal al-Druze region in the southern province of Suweida, where they constitute the vast majority of the local population. But there are also several Druze villages in other parts of the country, including in Idlib.
The Druze have largely kept out of the conflict in Syria, only taking up arms to defend their towns and villages.
The head of the Druze community in neighbouring Lebanon, Walid Jumblatt, said he had made contact with Syrian opposition factions and "influential regional forces", according to a news website run by his political party. This contact had yielded a "joint effort" to guarantee the safety of Druze villages in Idlib which had "stood by the revolution", it reported.
Last month, al-Nusra leader Abu Mohammed al-Julani told Al Jazeera that Druze would not be targeted, although he said representatives had been sent to their villages to "inform them of the doctrinal pitfalls they have fallen into".
However, activists in Idlib have said that Druze living in Idlib have been subjected to religious persecution by al-Nusra with several hundred forced to convert to Sunni Islam. The group was also accused of desecrating graves and damaging shrines.