Israel played down on Monday the risk from Syria's chemical weapons, in what appeared to be a new tack after threats to take military action to prevent the arsenal falling into Islamist hands.

Israel has been particularly worried that Hezbollah, the Iranian-inspired Shiite militia in neighbouring Lebanon, may gain access to the weapons should Syrian President Bashar al-Assad's grip slip amid a 16-month-old insurgency.

Israel's warnings on this spread war fears and bumped up demand for government-issued gas masks.

But since Syria last week acknowledged for the first time that it had chemical weapons, saying they were secure and would be used only as a last resort against "external aggression", the Israelis have been voicing cautious confidence.

"Nothing will happen," Defence Minister Ehud Barak told Israel Radio in an interview, joking that he would return his gas mask.

"In my opinion, no one in the world would dare to use chemical weapons against Israel. So nothing is going to happen."

Israel is believed to have the only nuclear arsenal in the region - something it has never acknowledged - giving it the ability to deter or retaliate against any non-conventional attack.

Hezbollah, a longtime Assad ally, has not commented on the speculation that it might want Syria's chemical weapons.

Israel and Hezbollah fought an inconclusive 2006 border war. Barak has since said that in any new conflict Israel would consider the whole of Lebanon fair game, given the militia's role in Beirut politics.

Some Israeli officials have also worried that radical Sunni Islamists among rebels fighting Assad may try to seize Syria's chemical weapons. Another suggested scenario is that Assad could use them against Israel in a suicidal last stand meant to secure his legacy in the Arab world.

Israel is technically at war with Syria and occupies the Golan Heights that it seized in the 1967 war and later annexed.

But the countries have not directly exchanged fire in three decades, and a parliamentary briefing last week by the Israeli armed forces chief about the risk of "uncontrollable deterioration" in Syria were interpreted by local media as a caution against opening a new fighting front with Assad.

"As long as the situation in Syria is still within Assad's control, Israel has no reason to worry," Eitan Haber, former spokesman for the late Prime Minister Yitzhak Rabin, wrote in the biggest-selling Israeli newspaper Yedioth Ahronoth.

"As long as they are in charge, the assumption is they will not use this doomsday weapon - with an emphasis on 'as long'."