Israeli authorities are distributing new gas masks to every citizen in an effort to guard against the possibility of chemical or biological attacks.

For many Israelis, gas masks and bomb shelters have been essential protections against possible rocket attacks from Gaza or militant groups in Lebanon.

Today Israel's biggest fear is the threat of attack from Iran - if not with a nuclear bomb, then with missiles possibly carrying chemical or biological weapons.

Over the next three years every one of Israel's 8 million citizens will receive a new gas mask for free.

Nearly 20 years ago Iraq fired scores of Scud missiles at Israel's two biggest cities - Tel Aviv and Haifa.

Four years ago, Hezbollah militants in Lebanon launched thousands of Katyusha rockets into the country's north.

Lieutenant Colonel Avital Leibovich from the Israeli Defence Force says it is ordinary citizens who are most at risk.

"There's a shift in focus of terrorists. The shift is towards the population," she said.

Israel recently simulated a biological and chemical attack as part of a military exercise to practice how authorities would respond in the event of the real thing.