The TASS news agency, citing the Russian defense ministry, said the US 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 US Central Command, part of the Department of Defense, had said that US forces struck an al-Qaeda facility north of Idlib in Syria in an attack aimed at the organization’s leadership.
A 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 the Russian military as saying that the United States carried out airstrikes in the region between Maarat Misrin and Kafer Haya in Idlib on Saturday.
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.
On Saturday, airstrikes on Idlib region stopped after the government agreed to a Russian-backed ceasefire following four months of clashes.