The Russian airforce has used a chemical weapons in Kahan Shaykhoun in Syria's northwest Syrian province of Idlib, activists have claimed in a video posted to Facebook.
In the video, uploaded on Wednesday, an activist wearing a gas mask shows a misshapen grenade with a small parachute attached to it.
He claims the grenade released a "foul-smelling" substance similar to chlorine or another poisonous gas.
The video shows tape sealing off a residential area where the activists say the grenade was dropped.
"The substance emitted from the grenade has not yet been identified," the activist states.
The smell is similar to that given off by the barrel bombs dropped by the Syrian airforce, the activist adds.
Syria's civil protection is not equipped to handle such dangerous substances, says an official who also appears in the video.
"In such cases, we evacuate the area and avoid approaching the weapons, before calling in expert squads to remove them."
Moscow launched air raids against the Islamic State militant group and rebels in Syria on 30 September in support of its ally, president Bashar al-Assad, a minority Alawite Shia Muslim.
The Russian missile strikes killed 595 people including 185 civilians in a month, the UK-based Syrian Observatory for Human Rights, a group monitoring the war, reported last week.
