The Russian military said the United States 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 on Sunday.
TASS news agency, citing the Russian defense 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.
On Saturday the U.S. Central Command, part of the Department of Defense, had said that U.S. forces struck an al Qaeda facility north of Idlib in Syria in an attack aimed at the organization's leadership.
The Syrian Observatory for Human Rights said air strikes pounded bases belonging to jihadist fighters in Syria's northwest. The UK-based monitor said the strikes, near the town of Maarat Misrin in Idlib province, killed more than 40 militants, including some commanders.
Interfax news agency cited Russian military as saying that the United States carried out air strikes in the region between Maarat Misrin and Kafer Haya in Idlib on Saturday.
U.S. air strikes have hit a number of Nusra commanders in northwest Syria in recent years.
Russia's defense ministry on Friday said that Syrian government forces would carry out a unilateral ceasefire in the de-escalation zone on Saturday morning.