Activists in Homs claim Syrian government forces used poisonous gas on a rebel-held neighbourhood, killing several people on Monday.
They say that more than 50 people in the district were exposed to the gas and many are in critical condition.
They claim the gas used was Agent 15, which lists suffocation, nerve paralysis, temporary blindness, and hallucinations amongst its symptoms. This is yet to be confirmed.
The attack comes a day after dozens of people were were reported dead following an air strike on a bakery in the town of Halfaya north of the central city of Hama. Videos uploaded by activists purported to show the aftermath of the attack, bloodstained bodies lying amid rubble and shrapnel.
The British-based Syrian Observatory for Human Rights put the number of dead at more than 60, although it said this number is expected to rise due to the number of people in critical condition.
Activists claim around 44,000 have been killed during the 21-month-conflict.