The OPCW says its team was not tasked with "identifying who is responsible for alleged attacks"
The global chemical weapons watchdog has said it is "very likely" that gas was used on civilians in Syria during attacks last year.
Lab analysis had confirmed the use of banned nerve agent sarin and chlorine in attacks in northern Syria, according to the Organisation for the Prohibition of Chemical Weapons (OPCW).
In a statement, the body said sarin was "very likely" used on 24 March 2017 in southern Ltamenah, in the Hama governate.
The OPCW also concluded chlorine was "very likely used as a chemical weapon" at Ltamenah Hospital and its surrounding area the following day.
It said the conclusions from its fact finding mission were based on witness testimonies, epidemiological analysis and environmental samples.
The statement added: "The collection of information and material, interviewing witnesses, as well as analysis of samples required a longer period of time to draw conclusions."
The OPCW also said the fact finding mission's mandate did not include "identifying who is responsible for alleged attacks".
"The fact finding mission's mandate is to determine whether chemical weapons or toxic chemicals as weapons have been used in Syria," the watchdog said.
However, it went on to say the inspectors had previously confirmed with a "high degree of confidence" the use of chlorine, sulfur mustard, and sarin as weapons in Syria.
The OPCW said its investigators were "required to study available information relating to allegations of use of chemical weapons in Syria, including information provided by the Syrian Arab Republic and others".
The findings come after at least 70 people were killed in April in an alleged chemical attack in the city of Douma, eastern Ghouta, which an aid group with links to opposition forces in the region said had been subjected to "one of the worst chemical attacks in Syrian history".