A chemical weapons watchdog group reported Wednesday that Syrian troops have "systematically and repeatedly" used chlorine as a weapon in the country's ongoing civil war.
The Hague-based Organization for the Prohibition of Chemical Weapons says its team found evidence on the ground that soldiers deployed the toxic gas on villages in northern Syria.
An Associated Press review of the full report noted that at least 13 people died in the attacks, and dozens were injured.
Chlorine was not on the list of chemicals Syria had to declare as part of a chemical disarmament agreement in 2013.
The OPCW based its report on testimony from victims, physicians, first responders and eyewitnesses, as well as medical records.
Although toxic, chlorine is not considered a chemical weapon. Other chemicals that could be used as weapons were required to be destroyed or shipped out of the country.
U.S. State Department spokeswoman Marie Harf squarely blamed President Bashar al Assad's government on Wednesday, saying it is the only entity with the helicopter force to carry out the attacks.
Human Rights Watch said in May that it had evidence Syrian military helicopters had dropped chlorine bombs on the same villages mentioned in the OPCW report.
The watchdog monitors the nearly 200 states that are party to the Chemical Weapons Convention, including Syria. Member countries agree to ban the use of chemical weapons.
