BEIRUT — Syrian rebels and government forces on Tuesday accused each other of launching toxic gas attacks on civilians..

Rebel sources provided video of people receiving treatment who they say were among the victims of a gas attack on Monday, but the images were not conclusive and neither claims by the rebels nor the government could be independently verified.

The accusations from both sides came amid heightened fighting around the contested city of Saraqib that has killed at least 20 people, activists and government media reported.

Rescuers and doctors in the rebel-held town reported dozens of cases of severe breathing difficulties, saying the symptoms pointed to a chlorine gas attack. Dr. Ibrahim al-Assad, a neurologist, said he treated 16 of the 29 cases brought to his hospital on Monday night, most of whom were women and children. Most were suffering from breathing difficulties, red eyes and wheezing, al-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 had died and eight others had 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.