The global chemical weapons watchdog has said it found traces of sarin following an attack in northern Syria in late March, days before a deadly strike using the same nerve agent in another Syrian town.
The Organisation for the Prohibition of Chemical Weapons said on Thursday that tests had revealed traces of "sarin or sarin-related chemicals" in Ltamenah after an attack on March 30 which injured 50 people.
No deaths were reported.
The organisation did not release further details.
Days later, on April 4, an attack in the north-western town of Khan Sheikhoun killed nearly 100 people. Syria has denied responsibility for that attack.
An OPCW-United Nations probe is expected to apportion blame later this month for the Khan Sheikhoun attack.