Five people were treated for "suffocation" on Sunday (February 4th) after Syrian regime airstrikes on the north-western town of Saraqeb, AFP reported.
The Syrian Observatory for Human Rights reported a "foul smell after regime helicopters struck several areas of the town in Idlib province, causing five civilians to suffer from suffocation".
It quoted residents and medical sources as saying "toxic gas" was used in the attack.
Regime airstrikes also killed six civilians in the town of Kafr Nabi, near Maaret al-Numan in the southern countryside of Idlib province, the Observatory said.
Four other civilians were killed in regime bombing on Maasarin and Maaret al-Numan, where the main hospital was hit by an unidentified airstrike.
The facility shut down until repairs could be carried out, the Observatory said.
The latest developments come as the US this week accused the Syrian regime of using chemical weapons on opposition forces near Damascus, an accusation the Syrian foreign ministry denies.
On Monday, at least 23 civilians — including four children — were killed as regime airstrikes pounded the opposition-held enclave of Eastern Ghouta near Damascus, the Observatory said.