Experts and political figures on Wednesday expressed growing doubts of Israel launching a military strike aimed at stopping Iran's nuclear drive, although such an attack hasn't been ruled out.

Talk of a pre-emptive Israeli strike on Iran has increased in recent weeks, in the run-up to the publication of a major report by the UN's atomic watchdog which was released late on Tuesday.

In the report, the International Atomic Energy Agency (IAEA) said it had "serious concerns regarding possible military dimensions" of Iran's nuclear programme, giving its clearest indication yet that Tehran may be developing nuclear weapons.

Israeli commentators believe the "unprecedented severity" of the report increases the likelihood of more stringent international sanctions against the Islamic republic and reduces the immediate chances of an Israeli strike.

"Israel can not afford to act alone against Iran," said Uzi Eilam, former head of Israel's Atomic Energy Commission.

"We must guard against hysteria. Iran is not an existential threat to Israel," he told army radio.

"Even if Iran manages to detonate a nuclear device as did North Korea, it will take six to seven years to equip its missiles with nuclear warheads," he added.

Some commentators said a strike on the concealed and fortified Iranian installations would pose a far greater challenge to Israel than in 1981 when it bombed Iraq's Osirak plant, and the strike in 2007 of a suspected nuclear site in Syria which has not been acknowledged by the Jewish state.

"Israel can not by itself stop Iran's nuclear programme, as was done in Iraq and, according to foreign media, in Syria," said former vice-premier Haim Ramon said on army radio.

Ramon said he doubted an air strike "could even put the Iranian nuclear programme back by five years," given the remoteness of the targets, their dispersion and Iranian defensive preparations.

"On the contrary, such a strike would give Iran an additional pretext to build a nuclear bomb" -- as a deterrent against Israel, he said.

"The Iranian nuclear programme is a problem for the whole world, Israel should not put itself in the front line to combat it."

Reuven Pedatzur, a political scientist at Tel Aviv University and military commentator, also raised questions about whether such an attack could significantly hamper Iranian efforts to secure a nuclear weapon.

"Israel does have the ability to bomb (Iran), but there is no guarantee that such an attack would delay Iran's nuclear programme, given the lack of information on the sites and the fact that they are so deeply buried," he told AFP.

But Efraim Kam, a researcher at the Institute for National Security Studies, said that as a last resort, an Israeli attack was "feasible, but very difficult."

However, there would be no such operation "without at least the tacit agreement of the United States," he said.

"The IAEA report confirms everything Israel has said in the past. It will facilitate international sanctions against Iran, which is the current option on the agenda," said Kam, a former military intelligence official.

Israel has refused to comment directly on the report, although several hours before it was released, Defence Minister Ehud Barak said the Jewish state had "not yet decided on a military operation against Iran."

But Iran's deputy chief of staff on Wednesday warned any attack by Israel would bring about "destruction" of the Jewish state and that its response would even be felt outside the Middle East.

Israel, which has the Middle East's sole if undeclared nuclear arsenal, suspects Iran of trying to develop atomic weapons under cover of a civilian nuclear programme.

Tehran denies that charge and has accused Israel of trying to sabotage its civilian nuclear programme and kill its nuclear scientists.