Syrian activists say civilians have suffered chlorine gas poisoning during an attack on the rebel-held town of Saraqeb in Idlib province.
The attack comes a day after Syria's former al-Qaeda affiliate claimed responsibility for the downing of a Russian warplane as it flew low over Saraqeb in northern Syria, apparently using a surface-to-air missile.
The pilot was killed after he ejected and exchanged gunfire with militants on the ground, the Russian Defence Ministry and a monitoring group said.
Hayat Tahrir al-Sham, or HTS, a powerful rebel alliance that publicly split from al-Qaeda last year, said it had used a man-portable antiaircraft system to shoot down the Su-25 fighter jet.
Saraqeb has come under heavy bombardment from Russian and Syrian warplanes in recent days as pro-government forces try to recapture a strategic highway linking Damascus to Aleppo.
In the hours after the Russian jet was downed, Moscow also claimed to have killed more than 30 militants in the area, Interfax reported.
The Syrian Civil Defence search-and-rescue group says three of its rescuers and six others were injured by chlorine gas in Saraqeb, which is less than 16km from the front line with government forces.
The Syrian American Medical Society says its hospitals in the area treated 11 patients for chlorine gas poisoning.
The Trump Administration last week accused Syrian President Bashar al-Assad's Government of producing and using "new kinds of weapons" to deliver deadly chemical poisons.
The charge came after at least two reported chlorine attacks near Syria's capital.
- AP, AAP, Washington Post