BEIRUT (AP) — Syrian opposition activists say an explosion outside an office belonging to an al-Qaida-linked group in the country's northwestern has killed at least 11 people.

The Britain-based Syrian Observatory for Human Rights and Smart news agency, an activist collective, said the blast occurred Friday on the southern edge of the rebel-held city of Idlib.

The blast comes a week after members of the al-Qaida-linked Hayat Tahrir al-Sham, Arabic for Levant Liberation Committee, or HTS, took over control of Idlib province and the surrounding countryside after forcing rival insurgents to accept a deal for a civil administration run by HTS in their areas.

The Observatory said 11 people were killed in the blast, including seven HTS members. Smart said 12 people were killed, many of them militants.