Israel on Thursday wound up nationwide testing of an SMS warning system against missile attack, sending texts to mobile phones in Jerusalem and other parts of the country, a military spokeswoman said.
The five-day exercise, which began on Sunday, took place to the backdrop of mounting speculation over a possible Israeli strike on Iran's nuclear facilities and a resulting Iranian counter-attack.
The army said that along with Jerusalem, Thursday's test included the Negev desert town of Arad, the northern cities of Afula and Hadera, and Upper Nazareth, a Jewish satellite of the Israeli Arab city.
A spokeswoman said that Nazareth itself, the largest Arab city in Israel, was not included in the test, with military sources explaining that when the system became fully operational it would cover all communities.
The army says the warning messages were being sent in Hebrew, Arabic, English and Russian.
They are meant to warn of an imminent missile attack by Iran or Lebanon's Hezbollah militia, which could become a reality if Israel decides to mount a military strike on nuclear facilities in Iran.
Israel believes the Islamic republic is trying to develop a military nuclear capability under the guise of its civilian programme which it says would pose an existential threat to the Jewish state.
Opponents of an Israeli attack said on Thursday that around 500 academics and retired military personnel had signed a petition calling on air force pilots to refuse to carry out a unilateral strike.
"I understand the far-reaching implications of this petition," a statement quoted one of the signatories, Tel Aviv University law professor Menachem Mautner, as saying.
"The possibility of a decision to attack Iran has been keeping me awake for weeks."
The statement warns that injury to Iranian civilians as a result of radioactive leakage from any of the targeted facilities could expose pilots to future war crimes charges.
"We issue this appeal to you out of a deep sense of concern and anxiety," the petition tells the Israeli airmen. "Our fate, our very future lies very much in your hands."
On Thursday, President Shimon Peres said Israel could not attack Iran without US help, in a television interview for his 89th birthday.
"It is clear that we can not do it alone," he said. "We can repel (an attack) but it's clear to us that we must act in concert with America, even if there are some issues of coordination and delays."
And later in the evening around 100 protesters marched in Tel Aviv denouncing any strike on Iran, an AFP photographer said.
"Enough of occupation (of Palestinian territories). No to an attack on Iran," chanted the protesters, including members of the opposition Meretz and Hadash parties.
Many protesters held up pictures of Prime Minister Benjamin Netanyahu and Defence Minister Ehud Barak with the caption "arsonists".
A poll, meanwhile, indicated that 61 percent of Jewish Israelis opposed a raid on Iran without US support.
The survey, published by the independent Israel Democracy Institute (IDI) think-tank, also said 57 percent of respondents believed talk of a pre-emptive strike is simply a tactic designed to pressure the Americans to take more resolute action against Iran.
"Most Jewish Israelis (56 percent) remain unconvinced that Israel will attack Iran without US cooperation in the near future," it added.
The IDI said the survey of 516 respondents was conducted by the Dahaf polling institute on August 7-8 and has a margin of error of 4.5 percentage points.
In recent weeks, the Israeli press has been flooded with reports citing anonymous top officials suggesting military action against Tehran's nuclear facilities is imminent.
But US Defence Secretary Leon Panetta on Tuesday said Israel had not yet reached a decision on whether to mount an attack.
US President Barack Obama has said Washington will stop Iran from "acquiring nuclear weapons" -- a step further down the line from Israel's red line, which says Tehran must not be allowed to acquire atomic weapons capability.
There is concern in Washington that a unilateral Israeli strike may not destroy Iran's underground nuclear facilities, could spark Iranian retaliation worldwide and may drag the United States into another war in the Middle East.