A helicopter has dropped barrels suspected to contain chlorine gas on a town in northern Syria, a doctor and rescuers have said.
About 30 people were affected by the attack, which took place in Saraqeb in Idlib province. It is not clear who was responsible.
Both sides in Syria’s civil war have been accused of, and denied, using chemical agents.
On Monday, a Russian military helicopter was shot down near Saraqeb.
Dr Abdel Aziz Bareeh, who works in Saraqeb, told the BBC that two barrels of chlorine gas were dropped on the town late on Monday.
“We know it’s chlorine because we were hit by it in the past and we are familiar with its odour and symptoms… We have 28 confirmed cases mostly women and children.”
Separately, a spokesman for Syria Civil Defence told Reuters that 33 people had been affected in the attack.
The organisation of volunteer rescue workers said it suspected the barrels contained chlorine but were unable to confirm it.
Chlorine is a common industrial chemical, but its use in weapons is banned by the Chemical Weapons Convention.
Symptoms typical of chlorine poisoning include sore eyes, irritated skin, breathing difficulties and bloody foaming from the mouth.
In 2013, the BBC found strong evidence suggesting residents of Saraqeb were subject to a chemical attack by government helicopters, something denied by the Syrian authorities.
The downing of the helicopter on Monday was the deadliest single incident for Russia’s military since its air campaign began last September. It is not clear who brought it down.
Pictures on social media, purportedly of the latest Russian helicopter downing, showed burning wreckage and bodies, with armed men milling around.
Meanwhile clashes are continuing near Aleppo, where rebels have launched an offensive to break a government siege.