Brigadier-General Itai Brun told a security conference photos of victims showing foam coming out of their mouths and contracted pupils were signs that nerve gas had been used.
"To the best of our understanding, there was use of lethal chemical weapons. Which chemical weapons? Probably Sarin", he said in comments broadcast on Army Radio.
The claim has been met by scepticism by the United States.
However, the US Secretary of State, John Kerry has said that Nato needs to work out how it will protect its members from any possible Syrian chemical weapons threat.
ITV News' Middle East Correspondent John Ray reports.