About 50 civilians were killed when missiles hit five medical centers and two schools in rebel-held Syrian towns on Monday, the United Nations and residents said.

The UN said, 'Such attacks are a blatant violation of international laws'.

Among the sites hit was a Medecins Sans Frontieres hospital, where seven people were reportedly killed. France said such acts constituted war crimes.

Activists have accused Russia of carrying out the strikes but there has been no independent confirmation.

Fourteen people were killed in the town of Azaz near the Turkish border when missiles slammed into a school sheltering families fleeing the offensive and a children's hospital, two residents and a medic said.

In a separate incident, missiles hit another hospital in the town of Marat Numan in Idlib province, in northwestern Syria, said the French president of the Doctors Without Borders Sans Frontières (MSF) charity, which was supporting the hospital.