He said that 46 people including eight children suffered from exposure to chemicals and have been hospitalised.
"Assad is interested in undermining the cease-fire,"a spokesman for the organization said".
The Russian defence ministry said the attack was launched from territory that former al-Qaeda militants control in the rebel stronghold of Idlib. Hospitals had discharged many people overnight. He said two people who were in critical condition have improved.
Syrian state TV aired footage late Saturday of the injured lying in hospital beds as doctors administered oxygen and other treatments.
The September 17 deal was meant to protect three million inhabitants in the Idlib region, more than half of which is held by HTS.
In addition to this, the governor of Aleppo, Hussein Diyab, reported an increase in the number of injured civilians in the attack, saying that this is confirmation of the possession of chemical weapons by terrorists, Sputnik reported.
Rebel officials, however, denied the charges and accused Syria of trying to frame them. The statement said the two exchanged views on "recent provocations that have been evaluated as aimed to undermine the Sochi agreement may continue and the need to be ready".
The projectiles landed in the al-Khalidiya neighbourhood, and wind caused gas to spread, Aleppo police chief Essam al-Shali told state television.More news: Mary Kom rewrites history by winning World Boxing Championship
State media said the army hit back at militants near the city but did not elaborate. There are no deaths, al-Shali said.
"There are often missiles on the city but this is the first time we smelled such a smell", the patient said without giving his name.
Russian Federation carried out the strikes after identifying the attackers' positions and finding evidence they could use such weapons again, Konashenkov said.
A cease-fire in Aleppo and Idlib has been fraying in recent days.
The first such attack came in April 2017, when US President Donald Trump ordered US Navy warships in the Mediterranean to fire a total of 59 Tomahawk cruise missiles at a Syrian airbase. The targeted area is opposition-held and home to extremist groups opposed to the truce such as the al-Qaida-linked Horas al-Din, which has described the deal as a "great conspiracy", and the Ansar al-Din Front.
The Russian defense ministry also accused the Civil Defense, also known as the White Helmets, of having a part in the alleged attack.
Rebel commander Abdel-Salam Abdel-Razak said the opposition doesn't possess poisonous gases or the capabilities to lob them.
Russia's defence ministry spokesman said earlier that Syrian rebel fighters used chemical weapons containing chlorine in an attack on Saturday on the government-controlled city of Aleppo. It also blamed Islamic State militants for using mustard gas.