Russia said on Saturday that opposition factions in Syria were preparing to stage a chemical weapons attack.
The Defense Ministry quoted unnamed sources as saying that the Hayat Tahrir al-Sham, formerly the al-Nusra Front, was preparing an attack against civilians in the northwestern Idlib province.
It is seeking to blame the possible attack on the Syrian regime, added the sources.
The Russian military cited its sources alleging that several containers with chlorine had been delivered to a local town and later taken to a nearby village.
The Defense Ministry also claimed that a private British contactor is helping the rebels to stage the attack.
The Russian statement comes several days after US National Security Adviser John Bolton warned Syria's regime against using chemical weapons and vowed a tough response if that happens.
"We now see plans for the Syrian regime to resume offensive military activities in Idlib province," he told a press conference during a visit to Jerusalem earlier this week.
"Just so there's no confusion here, if the regime uses chemical weapons we will respond very strongly and they really ought to think about this a long time."
In April the United States, France and Britain launched joint missile strikes on regime targets in response to a chemical weapons attack in the town of Douma that left scores dead.
