A leader in the National Liberation Front (NLF), an umbrella organisation of Turkey-backed rebels that includes the Free Syrian Army, has dismissed accusations they used poisonous gas to attack government-held Aleppo city.

The head of the NLF’s legislative office, Omar Huthayfa, told Al Jazeera the coalition does not possess poisonous gas and said the government is attempting to frame them.

“I believe that this is an act carried out by the government. We’ve seen it in Ghouta and in Khan Sheikhoun in the past and the international community remained silent,” Huthayfa told Al Jazeera.

“This is why the government has the audacity to continue accusing the opposition of carrying out such attacks when it knows that the opposition doesn’t possess even light weaponry for self-defence.”

His remarks came shortly after Russia – a key Damascus ally – and Syrian President Bashar al-Assad‘s government accused opposition fighters of launching chlorine gas attacks on Saturday night.

Russian military spokesman Major General Igor Konashenkov told reporters in Moscow that Russian warplanes destroyed rebel positions in northern Syria blaming them for the suspected poison gas attack.

“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.

The Britain-based Syrian Observatory for Human Rights and the Thiqa News Agency, an activist collective, said planes pounded rebel-held areas west and south of Aleppo city. The air raids were the first since the truce went into effect on September 17.

State news agency SANA reported “107 cases of breathing difficulties” in an updated toll on Sunday.

“We cannot know the kinds of gases but we suspected chlorine and treated patients on this basis because of the symptoms,” Zaher Batal, the head of the Aleppo Doctors Syndicate, told Reuters News Agency.

Batal said symptoms included difficulty breathing, eye inflammation, shivering and fainting. Hospitals had discharged many patients.

Al Jazeera could not independently verify whether an attack took place.

Earlier on Sunday, Russia‘s foreign ministry said in a statement that the attack had been launched from an area in Idlib’s de-escalation zone controlled by Hay’et Tahrir al-Sham (HTS), a former al-Qaeda affiliate that currently controls more than half of Idlib province.

“According to our preliminary information, confirmed in particular by symptoms of poisoning among the victims, the shells used to bombard residential areas of Aleppo were filled with chlorine [gas],” Russian Major-General Igor Konashenkov said.

Moscow said it would speak with Turkey as an opposition backer about the incident, the statement added.

For the past two months, the situation in the northwestern region of Syria has remained relatively calm.

In September, the leaders of Russia and Turkey signed a deal to establish a 15-20km de-militarised zone in Idlib, in a move that has put on hold a threatened all-out assault by the government on Syria’s last rebel-held stronghold.

As part of the deal, the NLF agreed to clear its heavy weaponry from the zone, which is meant to stretch from neighbouring Latakia’s northern suburbs all the way to the outskirts of Aleppo’s northwestern region.

But disarming the zone is only one aspect of the agreement, which also required the withdrawal of all so-called “radical” fighters from the area, including HTS.

According to Huthayfa, the latest claim made by the government may pave the way for a potential assault on Idlib.

Additional reporting by Farah Najjar.