Activists in Syria have claimed that government forces used chlorine gas in an attack on a village near the city of Hama.
Amateur footage uploaded by activists on Friday showed dozens of villagers from Kafr Zeta struggling to breathe as a result of a toxic substance.
Other footage online showed an unexploded canister suspected to contain chlorine gas. Al Jazeera cannot independently verify the images.
Rebels and the government blamed each other for what is supposed to be third alleged gas attack in the country in the past week.
Chlorine gas - used extensively in the First World War - attacks mucus membranes and can kill in high concentrations.
Syrian President Bashar al-Assad's forces have been repeatedly accused of using chemical weapons during the war in Syria. The deadliest known attack occurred in the rebel-held area of eastern Ghouta last year, leading to the deaths of hundreds of people.
UN inspectors found strong evidence of the use of sarin in the attack, but did not say who was behind it.
The attack triggered widespread condemnation and the Syria government, under international pressure, agreed to give up its chemical weapons stockpile.
Since chlorine also has industrial use, it was not included in the list of chemicals that Syria will have to give up under the agreement.
On Saturday, the head of the international team overseeing the disarmament process, said Syria has shipped out or destroyed approximately 80 percent of its declared chemical weapons material.
Sigrid Kaag, special coordinator of the joint mission of the UN and the Organisation for the Prohibition of Chemical Weapons (OPCW), said if the momentum was sustained, Syria should be able to meet its April 27 deadline to hand over all declared chemical agents.
"The renewed pace in movements is positive and necessary to ensure progress towards a tight deadline," Kaag said.