The global chemical weapons watchdog is to investigate allegations of chlorine gas attacks in Syrian villages that killed six and wounded dozens this month, a source told Reuters on Thursday.
The Organisation for the Prohibition of Chemical Weapons (OPCW) is to launch a fact-finding mission to examine reports of several barrel bombs in the northwestern Idlib region.
"It will be investigated," said a source, referring to the deadliest attack in the village of Sarmin, 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" in the four-year Syrian civil war, which has killed more than 200,000 people and displaced millions.
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.
Syria joined the Chemical Weapons Convention in 2013, agreeing to allow foreign weapons inspectors into the country and averting US-threatened air strikes after sarin attacks in the outskirts of Damascus killed hundreds.
The government of President Bashar al Assad has since handed over 1,300 tonnes of toxic chemicals and is destroying production and storage facilities.
The process of verifying that the chemical weapons programme has been eliminated is continuing.
US Secretary of State John Kerry said he was "deeply disturbed" by the reports of renewed use of chlorine gas, last used widely in World War One.
The use of industrial chemicals as weapons is banned under the 1997 Chemical Weapons Convention.
A group monitoring the Syrian civil war said on Tuesday government forces had carried out the poison gas attack that killed six people in the northwestern town of Sarmin, not far from the Turkish border.
Medics posted videos of children suffering what they said was suffocation, which could be caused by a number of toxic agents, including chlorine.
The OPCW team has a rolling mandate from the United Nations to investigate chemical weapon use in Syria, but will need to negotiate security arrangements with officials in Damascus if it plans on site investigations.