The US threw its support behind a recent report from the Organisation for the Prohibition of Chemical Weapons (OPCW) that says the Assad regime used chemical weapons in an attack on February 4, 2018, in Saraqib, Syria.
The body's investigation and identification team found that an elite unit of the Syrian Air Force dropped "at least one" cylinder containing chlorine over the city in north-west Idlib province during a period of intense fighting between the regime and rebel forces.
According to the report, no one was killed when the Tiger Forces dropped the barrel bomb containing chlorine gas on Al Talil neighbourhood.
But after the attack a dozen people were treated for symptoms consistent with chemical poisoning.
“This latest finding should come as a surprise to no one,” said Ned Price, spokesman for the US State Department.
"The Assad regime is responsible for innumerable atrocities, some of which rise to the level of war crimes and crimes against humanity."
The use of chlorine or any chemical substance in armed conflict is banned under the 1997 Chemical Weapons Convention.
The OPCW and The Hague are in charge of overseeing the application of the convention.
This is not the first time the body's investigative team accused the Assad regime of using chemical weapons.
Regardless, Syria repeatedly denied using chemical weapons during the decade-long civil war.
“The OPCW report is but the latest reminder of [President Bashir Al] Assad’s flagrant repudiation of the rule of law,” said Mr Price.
“All responsible nations must stand in solidarity against the deployment of chemical weapons by preserving the global norm against such use; and we must be ready to hold the Assad regime, and anyone who chooses to use these horrific weapons, accountable.”