More than 100 people have been wounded in a suspected toxic gas attack in Syria's Aleppo, which a health official said was the first such assault in the city.
Bashar al-Assad regime and its ally Russian Federation on Sunday claimed that an anti-regime armed group carried out a chemical attack from Idlib to Aleppo whereas the opposition elements and local sources disputed the allegations.
Syria's Arab News Agency, SANA, said the alleged chemical attack late Saturday was carried out by "terrorist groups positioned in Aleppo countryside" that fired shells containing toxic gases on three neighborhoods in Syria's largest city.
The air raids are the first since Russian Federation and Turkey agreed in September to create a demilitarised zone in adjacent Idlib to prevent a full-scale government offensive on Syria's last rebel-held province.
The Britain-based Syrian Observatory for Human Rights monitor said regime ally Russian Federation "likely" carried out the air strikes on a planned buffer zone around the opposition bastion of Idlib.
Earlier on Sunday, Moscow accused the militants of poisoning 46 people, including eight children in the attack, while regime news agency SANA said that 107 people had been injured.
A Syrian doctor at the Aleppo University Hospital said patients he treated were discharged less than two hours after being admitted, noting that they only displayed mild symptoms.
Patients suffered difficulty breathing, eye inflammation, shivering and fainting, he said.
No group had yet claimed the attack.
Rebel commanders and opposition figures discredited the government reports, denying they lobbed gas into Aleppo and accusing Damascus of seeking to undermine an existing cease-fire and efforts to kickstart political talks. "This is purely a lie", he tweeted.
State media said the army hit back at militants near the city but did not elaborate.
The deal to create the demilitarised zone staved off an army offensive against the Idlib region, including nearby parts of Aleppo and Hama provinces.
The insurgents are thought to have bombarded the Syrian city with shells filled with chlorine gas, Russia's Ministry of Defence said in a statement today. He says they came after government shells landed in rebel-held areas, violating a Russian-backed cease-fire.
Over the course of Syria's seven-year war, worldwide human rights groups have repeatedly accused belligerents - especially the regime - of carrying out chemical attacks.
The attack was apparently in retaliation to the earlier strikes in Aleppo.
The West has accused Damascus of using chemical weapons on several occasions, something Syria has consistently denied.
A joint commission of the United Nations and the Organisation for the Prohibition of Chemical Weapons (OPCW) has also accused the Islamic State group of using toxic gases.