JERUSALEM: Israel began the biggest civil defense drill in its history on Sunday, putting soldiers, emergency crews and civilians through rehearsals for the possibility of war at a time of rising tensions with Iran.

The five-day drill, code-named Turning Point III, will include simulated rocket and missile attacks on Israeli cities, including preparations for a nonconventional strike. Air-raid sirens are to sound across the country on Tuesday and for the first time, all Israeli civilians will be required to practice taking cover in shelters when the sirens go off.

It's the third consecutive year that Israel is holding the exercise, a direct result of its inconclusive 2006 war against Hezbollah guerrillas in Lebanon. During the conflict, the Iranian-backed Hezbollah fired nearly 4,000 rockets into Israel, and civil defense authorities, bomb shelters and air raid alarms were found to be unprepared.

Iran's development of long-range missiles, along with international concerns that Iran is developing nuclear weapons, have added to Israeli jitters. While the international community has been seeking a diplomatic solution to the Iranian nuclear issue, Israel has not ruled out military action.

Israeli leaders played down any connection between those tensions and this week's exercise, and officials have been at pains to allay fears among Arab neighbors, such as Lebanon and Syria, that it could be a cover for a military strike.

Speaking at the start of the weekly Cabinet meeting on Sunday, Prime Minister Benjamin Netanyahu described the drill as "routine" and said it was not connected to any specific event or to any intelligence warning.

"We are required to defend Israel, its cities, various installations, from the possibility of attacks by missiles, rockets or other weapons," he said. "I think the fact that Israel is preparing more from exercise to exercise and is capable of better protecting its citizens decreases the chance that we'll have to use these tools."

During the exercise, police, fire and ambulance services, hospitals, military rescue units and local authorities will practice dealing with various attack scenarios, including by missiles carrying non-conventional warheads, the national emergency service said in a statement.

It said the exercise would also include emergency sessions of the Cabinet to debate simulated events.

Defense officials said the exercises were designed to implement lessons learned from Israel's 2006 war with Hezbollah. It also incorporates experience gleaned from barrages of rockets fired into southern Israel by Palestinian militants in the Gaza Strip, Deputy Defense Minister Matan Vilnai said.

"We are holding exercises to meet the threats as we have experienced them in the past few years and as we may face them in the future," Vilnai told the radio. "It's the third time we've carried out this drill and I imagine that next year at this time there will be Turning Point IV."

Similar rehearsals were conducted in 2007 and 2008, but the military said this year's exercise would be "the largest and most comprehensive yet." Last year, sirens failed to function in parts of Tel Aviv and Jerusalem.

A state-of-the-art national civil defense control and command center will be inaugurated in this year's exercises.

Vilnai would not comment on whether the drill was meant to send a specific message to Iran but said every display or preparedness carried an element of deterrence.

"Our enemies long ago showed they believe that the home front is our Achilles heel," he said. "We are drilling there to prove that it is not."