Syrian government forces have used chemical weapons – probably nerve gas – in their fight against rebels waging a two-year-old uprising, the Israeli military's top intelligence analyst has claimed.

Brigadier-General Itai Brun told a security conference that photos of victims with foam coming out of their mouths and contracted pupils were signs the deadly gas had been used.

Brigadier-General Brun said: "To the best of our understanding, there was use of lethal chemical weapons.

"Which chemical weapons? Probably Sarin."

He said forces loyal to Syrian President Bashar al Assad were behind the attacks on "armed (rebels) on a number of occasions in the past few months".

The Syrian government and rebels last month accused each other of a chemical attack near the northern city of Aleppo.

On Monday, US Defence Secretary Chuck Hagel, who is visiting Israel, said US intelligence agencies were still assessing whether chemical weapons may have been used in Syria.

He said: "We, the United States, along with Israel have options for all contingencies and certainly the Syrian government's use of chemical weapons would be a game changer in crossing that red line."