France and Turkey denounce raids in which up to 50 people were killed as Assad casts doubt on prospects for 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.
Russia's Health Minister, Veronika Skvortsova, denied Moscow was responsible, saying its military had targeted Islamic State of Iraq and the Levant (ISIL) infrastructure and that she had no reason to believe it had bombed civilians.