BEIRUT: Gunmen early Saturday stormed an office of a Syrian paramedic group that is active in opposition-controlled areas, killing seven of its members and stealing two vehicles and other equipment in a northwestern region, the group and opposition activists said.

The Syrian Civil Defense group, more popularly known as the White Helmets, said in a statement that the attack happened in the early hours in the town of Sarmeen.

No one immediately claimed responsibility for the rare attack but it came amid tension in the area.

Sarmeen is in Idlib province, which witnessed clashes recently between Al-Qaeda-linked fighters and members of the ultraconservative Ahrar al-Sham group that ended with Al-Qaeda fighters capturing much of the region.

The Al-Qaeda-linked Hay’at Tahrir al-Sham said over the past weeks that its members have discovered sleepers cells of Daesh (ISIS) who were planning an attack.

Al-Qaeda’s affiliate, which used by to be known as the Nusra Front, has fought deadly battles with Daesh over the past years.

The Britain-based Syrian Observatory for Human Rights activist group said the seven were killed after being shot in the head, adding that the killings were discovered when volunteers from the White Helmets arrived to start a shift and found the bodies of their colleagues.

“Until now it is mostly likely a crime. It might also be an attack aimed to harm the image of the Nusra Front and to show that Idlib is not safe,” said Rami Abdel-Rahman, who heads the Observatory.

An opposition activist based in Idlib who has been providing the Associated Press with information about the province for years said the attackers used pistols equipped with silencers, adding that people living nearby did not notice anything unusual. The activist, requesting anonymity, said Daesh sleeper cells have been discovered in Sarmeen. He added that most likely members of Daesh carried out the attack to show that Idlib is not safe.

The activist said the Hay’at Tahrir al-Sham-linked Judicial Committee is investigating the case.

Sarmeen used to be a stronghold of the Jund al-Aqsa extremist group that clashed with Al-Qaeda last year before many of its members were allowed to head to areas controlled by Daesh, whom they are now fighting.

The Syrian first-responders have been known to risk their lives to save people from the civil war, now in its sixth year. The White Helmets group was widely considered likely to win last year’s Nobel Peace Prize.