The Syrian al Qaida branch and allied fighters from ultraconservative rebel factions have seized a village of President Bashar Assad's minority Alawite sect in central Syria.
The capture of Zaara, which was reported by activists and Syrian state media, is sparking fears of an outbreak of sectarian violence as activists say many families from the village are missing.
The development came as the International Red Cross was expected to deliver the first aid in almost four years to a cut-off Damascus suburb besieged by government forces.
The International Committee of the Red Cross (ICRC) was to bring humanitarian relief to Daraya in co-operation with the Syrian Arab Red Crescent and the United Nations, said ICRC spokesman Pawel Krzysiek.
It would be the first aid sent to rebellious Daraya since November 2012.
The UN estimates the suburb's current population is between 4,000 and 8,000 people.
The civil war in Syria, whose population is majority Sunni, was sparked by a crackdown on anti-government protests in 2011 but it has also developed a distinct sectarian undertone.
The Alawites are an offshoot of Shiite Islam and Mr Assad, an Alawite, has presented his side as defending the country's minorities against a Sunni Islam terror insurgency.
The Britain-based Syrian Observatory for Human Rights said families disappeared from Zaara after the militants overran the village.
Along with Syria's al Qaida branch, known as the Nusra Front, other hard-line factions that took part in the raid on Zaara included Ahrar al-Sham and Faylaq al-Rahman.
Separately, al Qaida's more powerful rival, Islamic State - also an extremist Sunni group - is in control of about a third of Syria's territory since its blitz in the summer of 2014 when it captured large swaths of Iraq and Syria.
Both al Qaida and IS are designated as terrorist organisations by the United Nations and were not part of a US-Russia-brokered cease-fire that was implemented at the end of February.
Syrian state media said "terrorists" killed a number of townspeople and abducted others, adding that they looted and destroyed many homes in Zaara.
World powers working to promote a resolution to Syria's civil war are planning to resume talks next week in Vienna, with UN-led, indirect peace negotiations between Syria's government and opposition representatives expected to follow some days later.
The Vienna talks aim to build on a US-Russia agreement announced this week to try to restore a nationwide cease-fire.