Secretary of State John Kerry voiced concern Sunday that the regime of Syrian President Bashar Assad has violated the Chemical Weapons Convention, which it signed earlier this year in a deal designed to avoid Western airstrikes on government assets.
In a statement, Kerry cited a recent Organization for the Prohibition of Chemical Weapons report which found that chlorine was used as a weapon "systematically and repeatedly" in attacks on three villages in northern Syria earlier this year during the country's three-year-old civil war.
"The report cites witness accounts indicating helicopters were used in the attacks--a capability the opposition lacks," Kerry said in a statement. "This strongly points to Syrian regime culpability."
Human Rights Watch said in May that it had strong evidence that in April this year Syrian army helicopters dropped bombs containing chlorine on the same rebel-held villages mentioned by the OPCW report.
Chlorine is a toxic industrial gas that is not specifically classified as a chemical weapon. However, the use of it as a weapon in large doses is considered a violation of the chemical weapons convention.
Kerry said in the statement the Obama administration is "concerned" the Assad regime was not completely honest when it declared and handed over its chemical weapons stockpile as part of the deal with the West, and that chemical attacks in civilian areas will continue.
"The Assad regime must know that it will be held to account for such use in the international community," Kerry said.
The statement comes at the same time the U.S. and other nations are considering striking at targets in Syria held by extremist militants fighting for the Islamic State of Iraq and Syria.