However, an Israeli official briefed on a meeting of Prime Minister Benjamin Netanyahu's security cabinet said the Jewish state believed the probability of it be targeted by Syria, its northern neighbour and long-time foe, was low.
"Following a security assessment held today (Wednesday), there is no reason for a change to normal routines," Netanyahu said in a statement. "We are, in parallel, preparing for any scenario."
That included a limited call-up of military reserve soldiers and deployment of an advanced missile shield in the north, the official said. Israel Radio said moblization of several hundred troops in intelligence and air defence had been authorized.
Army Radio reported the military was using all of its missile defences, which include the short-range Iron Dome, the mid-range Patriot and the long-range Arrow II.
Facing potentially imminent attack by the United States and other western powers over its alleged use of chemical weapons, Damascus has hinted it could shoot back at the Jewish state. Israel is also braced for possible rocket salvoes from Hezbollah, Syria's Lebanese militia ally.
Netanyahu said on Tuesday that Israel sought to stay out of the Syrian crisis but would respond forcefully to any attempt to attack it.
Israeli defence minister Moshe Yaalon said after the security cabinet meeting on Wednesday that Israel was "taking steps for just in case".
In a speech in Tel Aviv, Yaalon said Israel's "finger is not light on the trigger but whoever around us presumes they can challenge us by a threat will of course encounter our might if there is any attempt to hurt us or our citizens".
Assad, preoccupied with a 2-1/2-year-old uprising against his rule and facing a militarily superior enemy in Israel, has held his fire in the face of three Israeli air strikes in Syria this year on advanced weaponry.
However, many in Israel worry that he could lash out if he felt his back was against the wall, and long lines formed on Wednesday at gas mask distribution centres.
Israel has provided its citizens with equipment to cope with possible chemical or biological attacks since the 1991 Gulf War, when US-led troops drove Iraq out of Kuwait.
According to official figures, however, only about 60 per cent of Israelis collected their gas masks before the current tensions over Syria erupted. The Israeli postal service, which oversees mask distribution, said the number of orders phoned in by the public in recent days had quadrupled.
"We just want to be prepared. I'd say it's a bit of a surreal experience," a Jerusalem resident, who gave his name only as Tovy, said at a distribution centre. "I just really pray we're never going to really need to use it."