The Syrian Observatory for Human Rights said the deaths came yesterday in the village of Qalb Lawzah in Idlib province, most of which is now controlled by an alliance including Al-Nusra.
Observatory director Rami Abdel Rahman said villagers had protested after a Tunisian Al-Nusra leader "tried to seize a house belonging to a Druze resident of Qalb Lawzah, claiming he was loyal to the regime."
"Relatives of the owner of the house protested and tried to stop him, then there was an altercation and shooting," he added.
Abdel Rahman said some of the villagers had weapons and returned fire, killing three members of Al-Nusra.
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The Druze deaths were reported by Syria's official SANA news agency, which accused Al-Nusra and allied Islamist rebel group Ahrar al-Sham of an "appalling massacre committed against the people of Qalb Lawzah that claimed the lives of at least 30 people."
Quoting local sources, SANA said the dead included five members of a single family, three clerics and two women.
The Druze, followers of a secretive offshoot of Shiite Islam, made up around three percent of Syria's pre-war population of 23 million people.
They are concentrated mostly in the southern province of Sweida, the only Druze-majority region of Syria, but there are several Druze villages through other parts of the country, including in Idlib.
The community has been somewhat divided during the country's uprising, with portions fighting alongside the government, but some parts expressing sympathy for the opposition.
Mostly, the Druze have taken up arms only in defence of their areas, and have kept out of the fighting more broadly.
Writing on his official Twitter account today, he said contacts were underway to "calm the situation" after the deaths in Qalb Lawzah, without specifying further.