Story highlights The attack occurred in rebel-controlled Idlib province amid recent spikes in violence

The unidentified attackers stole vehicles and equipment, activists said

(CNN) 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. (Syrian Civil Defense White Helmets via AP) FILE PHOTO: In this photo provided by the Syrian Civil Defense group known as the White Helmets, Syrian Civil Defense workers search through the rubble after airstrikes in the village of Hass in the Idlib province, Syria, Oct. 26, 2016. SYRIA'S FIRST RESPONDERS: 'MOST DANGEROUS JOB IN THE WORLD'

The seven were killed after being shot in the head, the Britain-based Syrian Observatory for Human Rights said, which added that the killings were discovered when volunteers from Syrian Civil Defense arrived to start a shift and found the bodies of their colleagues. Sarmin is in Idlib province, which witnessed clashes recently between al-Qaida-linked fighters and members of the ultraconservative Ahrar al-Sham group that ended with al-Qaida fighters capturing much of the region.
Seven members of the White Helmets are shot dead by unidentified gunmen who stormed their office in rebel-held Sarmin, in northwestern Syria.