A woman and two children were killed and 16 people injured in the northern Syrian city of Aleppo on Saturday in what an anti-government violence monitoring group said was a gas attack by Syrian government forces.
Rami Abdelrahman, head of the Syrian Observatory for Human Rights, cited witnesses as saying that two gas bombs had been dropped from an army helicopter.
Doctors in the town of Afrin, where the injured were taken, told the Observatory that victims had "hallucinated, vomited, had excess mucus and felt their eyes were burning".
Reuters cannot verify such reports from Syria due to severe reporting and security restrictions.
A team of United Nations-led experts is waiting in Cyprus for the go-ahead to investigate three previous allegations of chemical weapons attacks in Syria, including one the government said was a poison attack by rebels in Aleppo last month.
The government of President Bashar al-Assad has rejected demands by the opposition that the inspectors be sent to investigate cases in Homs and Damascus where rebels say government forces used chemical munitions.
Aleppo's Sheikh Maqsoud district, where the two bombs were dropped on Saturday, is controlled by rebels. The Observatory distributed photos taken by opposition activists of remnants of what it said were the bombs.
It also sent photos of a dead woman and two children, who it said were both under two years old. None of the three had any visible injuries.
About 70,000 people have been killed in an uprising against four decades of Assad family rule that turned into a civil war after Assad's forces suppressed protests and opposition members took up arms. Both sides have been accused by rights groups of war crimes.