Seven members of the White Helmets rescue group were shot dead Saturday by unidentified gunmen who stormed the volunteers' office in northwestern Syria, the group and opposition activists said.
It was active in rebel-held eastern Aleppo before the territory was seized by forces loyal to President Bashar al Assad.
The group also known as the Syrian Civil Defense called for northern Syrian checkpoints to detain any vehicles bearing the White Helmets logo that were not verified.
It was not immediately clear whether the motives for the raid were political or purely criminal.
They receive funding from a number of Western governments, including Britain, Germany, the Netherlands and the United States.
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Abriya, who just finished three months of intense therapy , fell in love with the service dogs at the hospital. It just touched our heart, so we're just trying to do what we can to help".
The observatory's director, Rami Abdel Rahman, said: "Colleagues came in the morning for the change of shift and found them dead".
The civil defence, otherwise known as the "White Helmets", operates in rebel-held areas of Syria.
They have since gained widespread worldwide renown for their daring rescues, with footage often taken and circulated on social media.
Their detractors, including President Bashar al Assad's regime and his ally Russian Federation, accuse them of being tools of their global donors.
Sarmin is controlled by the Hayat Tahrir al Sham jihadist alliance, which was formed when the Nusra Front merged with other groups.
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