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.

The attackers also stole two vans, helmets and walkie-talkies, according to a statement from the group, which is formally known as the Syrian Civil Defense.

The Aleppo Media Center activist group also said seven volunteers were killed in an attack -- and posted video and photos of their funeral.

A procession of mostly men carried the dead to be buried, the images show. Many of the mourners wore the White Helmets badge and broke down in tears.

The Syrian Civil Defense called for northern Syrian checkpoints to detain any vehicles bearing the White Helmets logo that were not verified.

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