Using chlorine as a weapon is banned under the Chemical Weapons Convention, which Syria joined in 2013
The Russian military said Friday it has evidence of the use of chemical weapons by rebels in Syria's besieged eastern city of Aleppo.
"Experts from the Russian defence ministry have found unexploded artillery ammunition belonging to terrorists which contains toxic substances," the military said in a statement.
"After rapid analysis in a mobile laboratory, we have determined that the toxic substances in the rebels' ammunition are highly likely to be chlorine gas and white phosphorous."
The ammunition was discovered in the 1070 district on the southwestern outskirts of Aleppo, the statement said.
The Russian news agency Interfax said this zone was recaptured from the rebels by Syrian government troops a few days ago.
A more thorough analysis will be carried out by a Russian military laboratory accredited to the Organisation for the Prohibition of Chemical Weapons (OPWC), the Russian defence ministry said.
Syrian state media late last month accused rebel groups of having fired shells containing toxic gas into government-held parts of Aleppo, leaving dozens of people including civilians in need of treatment.
Last month, a joint OPWC panel concluded that Syrian government forces carried out three chlorine gas attacks on villages in 2014 and 2015.
Russia, however, has dismissed the findings of the joint investigative mechanism (JIM) as "unconvincing" and said no sanctions should be imposed on Syria for the chlorine gas attacks.
Using chlorine as a weapon is banned under the Chemical Weapons Convention, which Syria joined in 2013 under pressure from its ally Russia.
Aleppo, Syria's former economic capital, has been divided since 2012 between the western districts held by the regime and those in the east controlled by the rebels.
Russia has conducted a bombing campaign in support of the government of President Bashar al-Assad for more than a year.
But Moscow has suspended its air strikes on rebel-held eastern Aleppo since October 18, after international condemnation over its ferocious bombardment of the city.
It has also ordered several "humanitarian" ceasefires in Aleppo in recent weeks.