A monitoring group and opposition activists said six people, including three young children, were killed in the alleged regime gas attack in the village of Sarmin, in Idlib province.
"We are looking very closely into this matter and considering next steps," said Kerry, who led moves to force Syria to hand over its stock of chemical weapons last year to the international community for destruction.
"What is clear is that the Assad regime continues to flout international standards and norms, including, if these latest allegations are verified, the Chemical Weapons Convention."
Activists in Sarmin said chlorine gas had been used and published videos of a chaotic field hospital where disoriented victims coughed and held gas masks over their faces, as children cried in the background.
They also published videos of people trying to revive three young children who lay motionless in the field hospital.
After denying for years that it possessed a chemical arms arsenal, Syria finally joined the convention as part of the US-Russian brokered 2013 deal to dismantle its stockpile.
But Damascus did not have to declare its stocks of chlorine under that agreement because it is widely used for legitimate commercial and domestic purposes.
Use of the gas for military reasons would however be a breach of its undertakings under the Chemical Weapons Convention.
"Any and all credible allegations of chemical weapons use, including the use of toxic industrial chemicals, must be investigated," Kerry said, accusing the regime of President Bashar al-Assad of terrorizing Syrians "through indiscriminate airstrikes, barrel bombings, arbitrary detention, torture, sexual violence, murder and starvation."
"The Assad regime must be held accountable for such atrocious behavior," Kerry added.
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"We are looking very closely into this matter and considering next steps," said Kerry, who led moves to force Syria to hand over its stock of chemical weapons last year to the international community for destruction.
"What is clear is that the Assad regime continues to flout international standards and norms, including, if these latest allegations are verified, the Chemical Weapons Convention."
Activists in Sarmin said chlorine gas had been used and published videos of a chaotic field hospital where disoriented victims coughed and held gas masks over their faces, as children cried in the background.
They also published videos of people trying to revive three young children who lay motionless in the field hospital.
After denying for years that it possessed a chemical arms arsenal, Syria finally joined the convention as part of the US-Russian brokered 2013 deal to dismantle its stockpile.
But Damascus did not have to declare its stocks of chlorine under that agreement because it is widely used for legitimate commercial and domestic purposes.
Use of the gas for military reasons would however be a breach of its undertakings under the Chemical Weapons Convention.
"Any and all credible allegations of chemical weapons use, including the use of toxic industrial chemicals, must be investigated," Kerry said, accusing the regime of President Bashar al-Assad of terrorizing Syrians "through indiscriminate airstrikes, barrel bombings, arbitrary detention, torture, sexual violence, murder and starvation."
"The Assad regime must be held accountable for such atrocious behavior," Kerry added.
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