THE HAGUE: The global chemical weapons watchdog will investigate allegations of chlorine gas attacks in Syrian villages that killed six and wounded dozens this month, a source told Reuters Thursday.

The source at the Organization for the Prohibition of Chemical Weapons, who spoke on condition of anonymity, said a fact-finding mission will examine reports of several barrel bombs in Idlib province. “It will be investigated,” said the source, referring to the deadliest attack in the village of Sarmeen, where a barrel bomb hit a home, reportedly killing two children, their parents and wounding 90 residents.

The OPCW’s fact-finding mission concluded last year that the use of chlorine gas is “systematic.”

Both sides have denied using chlorine “barrel” bombs, which the OPCW said are dropped out of helicopters. The Syrian air force is the only party in the conflict known to have helicopters. The use of industrial chemicals as weapons is banned under the 1997 Chemical Weapons Convention.

The OPCW team has a mandate from the U.N. to investigate chemical weapon use in Syria but will need to negotiate security arrangements with Damascus if it plans on site investigations.

The fact-finding mission has issued three reports on the use of chlorine in Syria, most recently in December. Inspectors came under attack in May while looking into claims of chlorine gas attacks by Syrian forces in the central province of Hama.