"Assad is using chemical weapons in Syria," said Brigadier General Itai Brun, head of research and analysis in the army's military intelligence division, in remarks quoted on the army's official Twitter feed.
Brun spoke as US Defence Secretary Chuck Hagel wrapped up a three-day visit to Israel at the start of a regional tour, with concerns about the Syrian civil war and Iran's nuclear programme featuring heavily in talks.
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In remarks to the annual INSS security conference in Tel Aviv, Brun said the military had seen evidence indicating the use of chemical agents on several occasions, including in an incident on March 19.
"One of the characteristics of the recent period is the growing use by the regime of surface-to-surface missiles, rockets and chemical weapons," he said.
"To the best of our professional understanding, the regime has made use of deadly chemical weapons against the rebels in a number of incidents in the past few months," he said, referring to a March 19 incident in Aleppo province in which 31 people were killed, apparently by chemical agents.
Evidence could been seen in the physical symptoms suffered by those who had apparently been exposed to chemical agents, he said.
"The reduced pupils, the foam coming out of the mouth and other additional signs provide evidence that deadly chemical weapons have been used," he said, according to a transcript provided by the army.
"Which chemical weapons? Apparently sarin. The regime is also using chemical weapons that neutralise and are not fatal," he said.
Brun said the symptoms were observed in photographs taken of the affected area after the attacks in question.
Developed as a pesticide in Germany in 1938, sarin is a deadly and volatile nerve agent that is colourless and odourless.
In high doses, it paralyses the muscles around the lungs and prevents chemicals from "switching off" the body's secretions, so victims suffocate or drown as their lungs fill with mucus and saliva.
There were more than a thousand tonnes of chemical agents in Syria and "a lot" of warheads and missiles that could be armed with the deadly substance, Haaretz website quoted Brun as saying.
The White House has said the use of chemical agents in Syria would be a "game changer" but, although it is investigating such claims, it has yet to reach a definitive conclusion.
On Monday, Hagel said "our intelligence agencies are assessing what happened and what did not happen," refusing to discuss "contingency options" if the use of chemical agents were confirmed.
There was no immediate comment from Hagel's entourage on the army's claim.
Brun also spoke about a strike on a Syrian arms convoy, a day after Defence Minister Moshe Yaalon implicitly confirmed that the January incident was an Israeli operation to prevent the transfer of advanced weapons to militant hands.
"The SA-17 missile launchers that were bombed in Syria were going to be transferred to Hezbollah," the powerful Shiite Muslim party in neighbouring Lebanon and arch enemy of Israel, he said in remarks published on Haaretz's website.
Speaking at a press conference with Hagel on Monday, Yaalon said Israel had already "acted" to stop advanced Syrian weapons from falling into militant hands.
