Around 100 Syrians were hospitalised with breathing difficulties after the alleged chemical attack in the regime-held city of Aleppo on Saturday, state media and a monitor said.
Rebel commanders and opposition figures discredited the government reports, denying they threw gas into Aleppo and accusing Damascus of seeking to undermine an existing cease-fire and efforts to kickstart political talks.
"The planes of Russia's Aerospace Defense Forces carried out strikes on the detected artillery positions of terrorists in the area, from where the shelling of Aleppo civilians with chemical munitions was conducted late" Saturday, Konashenkov said.
Moscow said it would hold discussions with Turkey, which backs some rebel factions and helped broker a ceasefire in the insurgent stronghold of Idlib.
At least 107 people were injured after rebel groups fighting the Syrian government released toxic gas in a residential area in Aleppo, the official Syrian Arab News Agency claimed on Sunday.
"We at the National Liberation Front (rebel group) deny the criminal, lying regime's allegations that revolutionaries targeted the city of Aleppo with any missiles and especially not any containing chlorine gas", it said.
The shelling caused scores of people to suffer maladies ranging from fainting to severe breathing problems.
He told state TV that a total of 41 people (later revised to 50) had been admitted and accused rebels of using poisonous gas in the missiles they lobbed at the Aleppo neighbourhood.
He pointed to repeated warnings from Russian Federation that the White Helmets rescue volunteers in Idlib were staging chemical attacks in order to blame them on regime forces.
Announcing the demilitariazation agreement in September, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan said the creation of a 15- to 20-kilometer (approximately nine to 12 miles) demilitarized zone would prevent a "humanitarian crisis" in the northwestern province. "This is purely a lie", he tweeted.
The September 17 deal was meant to protect three million inhabitants in the Idlib region, more than half of which is held by an alliance led by jihadists of Al-Qaeda's former Syria affiliate.
In the absence of independent monitors, it is hard to corroborate gas attacks. The government has responded with counter attacks on rebel-held areas in the Aleppo countryside. He says they came after government shells landed in rebel-held areas, violating a Russian-backed cease-fire.
The joint UN-OPCW team has also blamed the Islamic State (IS) extremist group for using mustard gas twice in 2015 and 2016. At the same time, according to the French government, during 2012-2017 the chemical weapons in Syria were used at least 130 times.
Russian Federation accused Hayat Tahrir al-Sham militants of firing the chemicals at the town, at first claiming 12 were killed in the attack before lowering the death toll to zero.