The Organisation for the Prohibition of Chemical Weapons, which is overseeing the destruction of Syria's chemical stockpile, said inspectors had information pointing to chlorine gas-like chemicals having been used despite having been forced to cut short their mission after the attack.
"Despite the grave incident which prevented the fact-finding mission from conducting an important field visit, the team was able to prepare a preliminary report," the organisation said in a statement.
"The information that was available to the fact-finding mission lends credence to the view that toxic chemicals - most likely pulmonary irritating agents, such as chlorine - have been used in Syria," the body said.
The inspectors, from a joint OPCW/United Nations fact-finding team, were travelling to the central province of Hama to investigate allegations of illegal chlorine attacks by government forces when their convoy came under attack.
No team members were injured in the attack, which the Syrian government blamed on rebel fighters.
President Bashar al-Assad, whose forces have been battling rebels trying to unseat him for more than three years, agreed last year to hand over Syria's entire chemical weapons stockpile after hundreds of people were killed in a sarin gas attack near Damascus.