Russian Foreign Ministry has said that Syrian rebels used chemical weapons, killing 16 people and injuring 100 others.
The ministry said Tuesday’s attack represented an “extremely dangerous” development in the two-year Syrian crisis.
It said the rebels detonated a munition containing an unidentified chemical agent in the province of Aleppo. It did not give further details.
Syria’s state-run news agency has also accused the rebels of the attack in the town of Khan al-Assal, saying 25 people died, but the rebels say government forces fired the weapon.
Russia said that the evidence of rebels getting hold of weapons of mass destruction had taken the confrontation to a new stage.
Russia has been the main ally of President Bashar Assad’s regime since the start of the uprising, in which more than 70,000 have died.
Abou Firas, spokesman for the Revolutionary Council in Aleppo city, denied that rebels used chemical weapons, saying it was “part of the regime propaganda to mislead the public opinion”.
“It is just a counter-claim to what rebels had been saying about the threat of chemical weapons being used by the regime,” Abu Firas told Al Jazeera.
Louay al-Mokdad, media and political coordinator of the opposition Free Syrian Army, also told Al Jazeera these were “false claims”, accusing the regime of being behind the reported attack.
The head of an international anti-chemical weapons body said on Tuesday he had no independent information about any use of such arms in Syria.
“Of course we have seen those reports and we are closely monitoring the situation,” Ahmet Uzumcu, head of the Organisation for the Prohibition of Chemical Weapons (OPCW), told a seminar in Vienna.