The Russian military said on Sunday that the United States had carried out air strikes in Syria's Idlib de-escalation zone in breach of previous agreements, inflicting numerous casualties and endangering a ceasefire, Russian news agencies reported.

TASS news agency, citing the Russian defence ministry, said the United States had forewarned neither Russia nor Turkey about the strikes.

It added that Russian and Syrian warplanes had not carried out raids in the region recently.

Russia's defence ministry said on Friday that Syrian government forces would carry out a unilateral ceasefire in the de-escalation zone in Idlib region on Saturday morning.