Radi Saad, from the chemical weapons team of the White Helmets civil defense group that operates in rebel-held parts of Syria, told Reuters three of the nine people who suffered from "suffocation injuries" were rescuers responding to the incident.
The Syrian government denies using chemical weapons.
The Observatory says 16 people were killed while the activist-run Ghouta Media Center put the toll at 17 dead.
It released a video of its workers rushing to rescue victims from the debris on Tuesday.
The U.N. mission in Damascus warned Tuesday of "dire consequences" to the humanitarian crises in Syria, identifying seven areas needing urgent relief.
Syria's multi-sided war has drawn in armies and insurgents from around the world, aggravating a conflict which began as an uprising against Assad's rule.
However, Russian and Syrian government forces have continued to bombard Idlib, with observers fearing a repeat of the crushing of opposition forces in Aleppo in 2016. The monitoring group said the campaign against Ghouta has killed at least 350 civilians, including more than 80 children.
Injured Nick Kyrgios feels disappointed after Davis Cup loss
Kyrgios - who had won six of his past seven rubbers - now has a 9-6 Cup singles record while Zverev improved his tally to 3-4. Two of those five-set losses could have gone either way (but) that's tennis", Hewitt said.
Two Turkish soldiers were killed in mortar attacks in Syria's Afrin district and Idlib province, according to a military statement on February 5. The military said the soldier was killed late Monday by a mortar-and-rocket attack that also wounded five Turkish soldiers and a civilian military contractor.
The Syrian state news agency SANA said three people were killed in the government-controlled Old City in Damascus when rebels launched a series of missiles.
United Nations officials in Syria called for fighting to stop to enable aid deliveries and the evacuation of sick and wounded, listing seven areas of concern including northern Syria's Kurdish-led Afrin region, being targeted by a Turkish offensive. First, he used his handgun against attackers and then blew up himself with a hand grenade.
The media campaigns targeting Russian Federation and its policy on Syria have been launched in order to undermine the outcome of the recent Syrian National Dialogue Congress in Sochi, the Moscow platform of the Syrian opposition said in a statement.
The YPG has been an important USA ally in the war against Islamic State militants, but Ankara sees it as an extension of the Kurdistan Workers Party (PKK), which is listed as a terrorist group by Turkey, the European Union and Washington.
Rouhani was quoted as telling his Russian counterpart Vladimir Putin in a phone conversation that "tensions in northern Syria do not benefit anybody".
The region has been under intense attack since the end of December as the government of President Bashar Assad struggles to bring it under control.