Around 35 civilians, mostly children, were killed in Syria's Idlib province on Wednesday after a school in Haas village was hit by airstrikes. According to the Syrian Observatory for Human Rights, the air raids are believed to have been carried out by Russian aircraft, Al Jazeera reported.

A report on Syrian state television claimed that a number of rebel fighters had been killed when their positions in Haas were hit by the airstrikes. However, the report did not mention the school. An activist said the first "rocket" hit the school as students were leaving to go home after the administration decided to wind up early as the airstrikes had started. Some of the injured are in critical condition, and it is feared that the toll will rise.

The United Nations Children's Fund said this may be the "deadliest attack on a school since the [Syrian] war began more than five years ago". "This is a tragedy. It is an outrage. And if deliberate, it is a war crime," said Unicef Executive Director Anthony Lake. "Children lost forever to their families…teachers lost forever to their students…one more scar on Syria's future."

Russian Ambassador to the United Nations Vitaly Churkin said: "It's horrible, I hope we [Russia] were not involved. It's the easiest thing for me to say no, but I'm a responsible person, so I need to see what my Ministry of Defence is going to say."

Idlib is controlled by an alliance of rebel groups called the the Army of Conquest. The Syrian Observatory said the frequency of airstrikes in the province had increased of late. The Bashar al-Assad government, with the support of Russia, Iran and a few militias, has drawn criticism from rights groups and the West for its indiscriminate attack in civilian regions. Idlib is the highest populated rebel-held region, located near Aleppo in northwest Syria.