Russian warplanes on Sunday attacked rebel-held areas in northern Syria for the first time in weeks, reports The Associated Press.
The strikes came after Syrian officials said more than 100 people were treated at hospitals for a suspected poison gas attack in the northern city of Aleppo that Damascus and Moscow blamed on rebels.
The rebels, who denied carrying out any poison gas attacks, accused the government of trying to undermine a truce reached by Russia and Turkey in September during a summit in the Russian city of Sochi.
Russian military spokesman Maj. Gen. Igor Konashenkov told reporters in Moscow that Russian warplanes destroyed militant positions in northern Syria blaming them for the attack with poison as on Aleppo, according to AP.
On Saturday, Syrian media reported that Syrian rebels fired projectiles containing poison gas on the al-Khalidiya neighborhood of Aleppo.
Syria’s official news agency SANA said the alleged chemical attack late Saturday was carried out by "terrorist groups positioned in Aleppo countryside".
Syria's forensic medicine general director, Zaher Hajo, told AP on Sunday that all but 15 of the 105 people who were treated have been discharged. He said two people who were in critical condition have improved.
The Britain-based Syrian Observatory for Human Rights said 94 people were treated, with 31 remaining in hospitals.
Both the Syrian regime and the rebels fighting it have accused each other throughout the Syrian civil war of using poison gas.
A joint team from the United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) accused Syria's government of using chlorine gas in at least two attacks in 2014 and 2015, and the nerve agent sarin in an attack in April 2017 in the town of Khan Sheikhoun that killed about 100 people.
The UN-OPCW team also determined that the Islamic State (ISIS) jihadist group used mustard gas in Syria twice, in 2015 and 2016.
Such chemical attacks in 2017 and earlier this year led the US to launch punitive strikes against Syrian forces.
Syria denies that it has ever used chemical weapons against civilians and has received backing on this issue from Russia, its close ally.