Israel has explicitly accused Syria of using chemical weapons against rebel forces.
Brigadier General Itai Brun told a security conference in Tel Aviv on Tuesday that photos of victims showing foam coming out of their mouths and contracted pupils were signs deadly gas had been used.
He believes the chemicals were likely to be sarin.
It is the first time Israel has accused Syria of using its stockpile of chemical weapons, Reuters reports.
The Syrian government and rebels last month accused each other of launching a chemical attack near the northern city of Aleppo.
The United States has said it will not tolerate the use of chemical weapons in Syria.
Secretary of State John Kerry, who is in Brussels, has told NATO members that the alliance needs to consider how it will to respond if the claims are confirmed.