The rescue workers were killed in a raid by unknown assailants on their base in a militant-held area
Unidentified attackers shot dead seven members of Syria's White Helmets rescue service early on Saturday during a raid on their base in a militant-held northwestern town, the group said.
The attackers struck in the town of Sarmin, nine kilometres east of the city of Idlib, which is controlled by the Hayat Tahrir al-Sham Islamist alliance.
"The civil defense center in Sarmin was the target of an armed attack by an assailants in which seven volunteers were killed," the White Helmets said in statement.
"Two minibuses, some white helmets and walkie-talkies were stolen."
It was not immediately clear whether the motive was for the raid was political or purely criminal.
The Syrian Observatory for Human Rights said the seven volunteers had all been killed by bullets to the head.
Colleagues came in the morning for a change of shift and found them dead, Observatory head Rami Abdel Rahman told AFP.
Syrian opposition activists are posting pictures purportedly showing the White Helmet volunteers who were killed pic.twitter.com/1yfcepD6Rh
— Raf Sanchez (@rafsanchez) August 12, 2017
The White Helmets emerged in 2013. They operate a rescue service in rebel-held parts of Syria, which have been subjected to fierce bombardment by the government and Russia's air force that has levelled whole city districts during the country's civil war.
They have since gained international renown for their daring rescues, often filmed and circulated on social media, and were nominated for the 2016 Nobel Peace Prize.
Although they work exclusively in rebel-held areas, they are non-partisan.
Their detractors, including President Bashar al-Assad's government and his ally Russia, accuse them of being the tools of their international donors.
They receive funding from a number of Western governments, including Britain, Germany, the Netherlands and the United States.
Critics also accuse them of harbouring rebel fighters, including Islamist militants, in their ranks.
According to unverified statistics compiled by the White Helmets, volunteer rescuers have saved more than 85,000 civilians since the group's inception.
It currently has over 3,000 volunteers conducting rescue missions across rebel-held parts of Syria.