First female White Helmets rescuer killed in Syria
It said rescue worker Sobhiya al-Assad was killed along with several members of her family when bombing raids hit their house in the town of Kafr Sejna.
"She's the first female #WhiteHelmet volunteer to be killed. Her service will never be forgotten," the rescue group said.
Idlib, most of which is held by fundamentalist militants and allied rebels, has been regularly battered by Syrian government airstrikes in recent months.
A vast majority of its 3,700 members are men, but it does include female rescuers.
The group emerged in 2013, when Syria's conflict was nearing its third year, and operates in battered opposition-held zones.
Since their founding, more than 200 of their volunteers have died and another 500 have been injured.
The group's motto - "To save one life is to save all of humanity" - comes from a verse in the Quran, although the White Helmets insist they treat all victims, regardless of religion.
Some members have received training abroad, returning to instruct colleagues on search-and-rescue techniques.
The group receives funding from a number of governments, including Britain, Germany and the United States, but also solicits individual donations to purchase equipment, including their signature hard hats which cost $145 each. The group announced an international funding shortfall in February.
Last year, a Netflix documentary called The White Helmets won an Academy Award for best short documentary.
The Syrian conflict began when the Baath regime, in power since 1963 and led by President Bashar al-Assad, responded with military force to peaceful protests demanding democratic reforms during the Arab Spring wave of uprisings, triggering an armed rebellion fuelled by mass defections from the Syrian army.
According to independent monitors, hundreds of thousands of civilians have been killed in the war, mostly by the regime and its powerful allies, and millions have been displaced both inside and outside of Syria. The brutal tactics pursued mainly by the regime, which have included the use of chemical weapons, sieges, mass executions and torture against civilians have led to war crimes investigations.