Air strikes by Syrian or Russian warplanes killed at least 26 people, most of them school children, in a village in Syria's rebel-held Idlib province, rescue workers and a monitoring group said.

The raids hit a residential area and a school in Haas village, the Syrian Civil Defence rescue workers network said on its Facebook account.

A report on Syrian state TV quoted a military source saying a number of militants had been killed when their positions were targeted in Haas, but did not mention a school.

Syria's civil war pits President Bashar al-Assad, backed by Russia, Iran and Shi'ite Muslim militias from Lebanon, Iraq and Afghanistan against an array of mostly Sunni Muslim rebel groups including some backed by Turkey, Gulf monarchies and the United States.

Idlib, near Aleppo in northwest Syria, contains the largest populated area controlled by rebels, both nationalist groups under the banner of the Free Syrian Army and Islamist ones including the former al Qaeda affiliate Jabhat Fateh al-Sham.

The Civil Defence network, which operates in rebel-held areas in the country, said 20 of the dead in the attacks were children.

Photos taken at the scene showed buildings with walls reduced to rubble, including what appeared to be the school with upturned desks and chairs covered in dust.

The Syrian Observatory for Human Rights, a British-based war monitor, said the warplanes had struck several locations in Haas including an elementary and middle school, killing at least one teacher as well as the children.

It gave a lower toll of 15 children killed.

Western countries and international human rights groups have regularly highlighted the high number of civilian deaths reported after Syrian and Russian air strikes.