°®Âþµº

Rebel sources had released a video showing people receiving treatment, claiming they were victims of a regime gas attack. But the claims could not be independently verified.

Rescuers and doctors in rebel-held Saraqib, a town in the northwestern Idlib province, about 40 kilometres [25 miles] southwest of Aleppo, reported dozens of cases of severe breathing difficulties, saying the symptoms pointed to a chlorine gas attack.

At least 33 people, mostly women and children, were affected by the gas, a spokesman for the Syria Civil Defence said.

"Medium-sized barrels fell containing toxic gases. The Syrian Civil Defence was not able to determine the type of the gas," Reuters reported the spokesman as saying.

A neurologist, Ibrahim al-Assad, said he treated 16 of 29 cases brought to his hospital on Monday night, most of whom were women and children.

One elderly man needed critical care but most of the casualties were suffering from breathing difficulties, red eyes and wheezing, Assad said.

He said first responders smelled the gas at the site of the bomb attack, which he described as a busy shopping area near an ice cream shop.

Rebels and activists have reported chlorine gas attacks in the town before, but the lack of chemical labs or independent testers makes it difficult to verify these claims. The government denies that is has launched chlorine gas attacks.

Syrian state media later reported that five people died and eight others experienced breathing difficulties after artillery shells laced with toxic gases landed on the old city of Aleppo. It said the shells were launched by rebels.

Meanwhile, fighting intensified around Aleppo and its neighbouring provinces since the government sealed off the final route into rebel-controlled neighbourhoods of the city.

The UN said the encirclement of rebel-held areas of deeply divided Aleppo traps nearly 300,000 residents, making it the largest besieged area in war-torn Syria.

Agencies contributed to this report.