U.S. Secretary of State John Kerry
U.S. Secretary of State John Kerry Reuters

U.S. Secretary of State John Kerry on Sunday warned the regime of Syrian President Bashar Al-Assad that it would be held to account for using chlorine gas against civilians.

According to AFP, Kerry pointed to a report by the Organization for the Prevention of Chemical Weapons (OPCW) that concluded with "a high degree of confidence" that chlorine has been used systematically and repeatedly as a weapon in northern Syria.

His comments came as Damascus said it had turned over all its chemical weapons, had cooperated fully with the OPCW and adhered to the Chemical Weapons Convention.

Kerry noted that the OPCW report had cited witness reports that helicopters were used in the chlorine gas attacks, which he said "strongly points to Syrian culpability" because the rebels do not have helicopters.

The report also mentioned that there were additional attacks in August which witnesses said resembled those in which chlorine gas use was confirmed, Kerry said, according to AFP.

"This finding, coupled with deep concerns regarding the accuracy and completeness of Syria's declaration to the OPCW, raises especially troubling concerns that continued chemical attacks on the Syrian people by the regime could occur," he said.

"The United States is gravely concerned about the findings in this report, which point to a violation of the Chemical Weapons Convention," added Kerry. "The Assad regime must know that it will be held to account for such use in the international community."

Activists in Syria said several months ago that over 100 people had been killed in a chlorine gas attack in the town of Talmenes in Idlib province, and the United Nations Security Council has called for an investigation into the alleged attack. Since then there were reports of other such attacks.

Kerry himself said a few months ago that he has seen “raw data” indicating that the Syrian government has used chlorine gas as a chemical weapon in a “number of instances” in recent months.

Syria has emphatically denied that it carried out chlorine gas attacks against civilians.