France and Turkey have called the bombing of two schools and five hospitals in Syria "war crimes", while hopes for a ceasefire faded as Bashar al-Assad played down prospects of a truce.

Up to 50 civilians, including children, died when missiles hit at least five medical buildings and two schools in the Aleppo and Idlib provinces on Monday.

UN Secretary General Ban Ki-moon said the raids violated international law and "cast a shadow" over efforts to end Syria's five-year civil war. He did not say who was responsible for the attacks but groups monitoring the conflict suspected the strikes were carried out by Russia, an ally of the Syrian regime.

French Foreign Minister Jean-Marc Ayrault said attacks on health facilities in Syria by the regime or its supporters were "unacceptable and must stop immediately".

Turkey on Monday separately accused Russia of "an obvious war crime" and warned that there would be consequences if Russia did not immediately end such attacks.

The United States, which like the UN did not specify who carried out the strikes, said two civilian hospitals were hit in northern Syria: one run by medical charity Medecins Sans Frontieres (MSF) and another in the opposition-held Azaz city.

"That the Assad regime and its supporters would continue these attacks ... casts doubt on Russia's willingness and/or ability to help bring to a stop the continued brutality of the Assad regime against its own people," the US State Department said.

PHOTO CAPTION

People gather around the rubble of a hospital supported by Doctors Without Borders (MSF) near Maaret al-Numan, in Syria's northern province of Idlib, on February 15, 2016, after the building was hit by Russian air strikes.

Al-Jazeera