According to a report by CNN, the unknown gunmen stormed the volunteers' office in northwestern Syria to carry out the attack.

The attack occurred in the city of Sarmin in Idlib province, which is controlled by Hayat Tahrir Al-Sham, a coalition of Salafi jihadist groups that includes Fateh al-Sham.

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.

The White Helmets have brought to light the scale of the Syrian conflict in a painfully visceral way, documenting their recovery operations through video and photo.

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