The White Helmets reported on Sunday night that the incident took place in Saraqeb, an opposition-held town less than 16 kilometers from the front line with pro-Assad regime loyalists.
The rescue group, which has been accused of being anti-regime, posted videos of their response — extinguishing fires at the central hospital in Maarrat al-Numan, hosing off people, and intubating the victims' airways.
Rudaw could not independently verify the authenticity of the video.
#Saraqeb @SyriaCivilDef teams respond to an attack with chlorine gas. 9 injured including 3 White Helmet volunteers. Attacks like this, in violation of UN Security Council resolutions, happen with impunity. @BBCWorld @cnnbrk pic.twitter.com/mLtfQ0OMnv
— The White Helmets (@SyriaCivilDef) February 4, 2018
"... a bad smell spread after the targeting and residents and doctors accused the regime forces of targeting Saraqeb by gases which resulted in the asphyxiation of the civilians," reported SOHR.
The Syrian Observatory for Human Rights is a UK-based conflict monitor that relies on local reportages.
The Observatory added that Idlib witnessed "continuous, intensive, and violent bombardment."
Saraqeb is 265 kilometers north of Damascus and just southwest of Aleppo.
Over the past week, opposition groups linked to al-Qaida have been advancing eastward toward Syrian-regime lines.
A Russian plane was shot down by rebels in Sarape on Saturday. Moscow confirmed its pilot was killed after he ejected, landed, and exchanged handgun fire with the opposition fighters.
Moscow has provided air support for Bashar al-Assad's regime in the Syrian conflict.
US Defense Secretary Mattis was asked on Friday about the weaponization of gasses in Syria.
"It has [been weaponized," claimed Mattis.
"We are even more concerned about the possibility of sarin use, the likelihood of sarin use, and we're looking for the evidence," he told reporters at the Pentagon.
Russia and the Syrian regime deny that they use chemical weapons in the seven-year civil war.
To the north on Thursday, a Turkish column of vehicles in the south of Aleppo governorate came under fire from regime loyalists.
There were unconfirmed reports of Syrian war planes striking near the convoy. Russia did not claim any role in the strikes.
More than 270,000 have been displaced in Idlib since the Syrian government launched its fresh assault on December 15, according to the UN.
UN-backed investigation teams for gas attacks in Syria previously have complained of the ability to get to the alleged sites, with Russia calling for a more neutral process to investigate.
