The cause of the incident, which occurred on Monday, remains unknown, the agency reported citing Idlib's civil defense service. Many injured people remain in a serious condition.
The photos of the ruined building have emerged in the internet.
Idlib is one of four de-escalation zones created after relevant agreements were reached by Iran, Russia, and Turkey, peace guarantor states in Syria during the Astana reconciliation talks last year.
Syria has been engulfed in a civil war since 2011, with government forces fighting numerous opposition factions and terrorist groups. The international community has taken a number of steps aimed at settling the crisis, including through negotiations in Geneva and Astana, as well as the Syrian National Dialogue Congress which took place in the Russian city of Sochi in January.