At least 35 people, many of them schoolchildren, were killed on Wednesday in air strikes on a rebel-held village in northwestern Syria. The United Nations has called for an immediate probe into the attack.

The raids hit a residential area and a school in the village of Hass, in Idlib province. The Syrian Observatory for Human Rights said either Russian or Syrian warplanes carried out six strikes, including the one on the school complex. But Russia has denied any involvement and demanded an immediate investigation.

"It's a lie. Russia has nothing to do with this terrible tragedy, this attack. We demand maximum attention on this tragedy and an immediate investigation," said Maria Zakharova, spokesperson of Russian Ministry of Foreign Affairs.