Meanwhile, International Atomic Energy Agency chief Mohamed ElBaradei is under fire from Western quarters that he is too soft on Iran.

Iran is certain to be a key topic of discussion at the week-long conference at IAEA headquarters in Vienna. Iranian vice president and head of the Atomic Energy Organisation (AEOI) Reza Aghazadeh will address the gathering.

US Energy Secretary Samuel Bodman and Sergei Kiriyenko, director of Russia's Federal Atomic Energy Agency, are also attending.

French Foreign Minister Bernard Kouchner warned Sunday that the world should brace for a possible war over the Iranian crisis but seeking a solution through talks should take priority.

"We have to prepare for the worst, and the worst is war," Kouchner said in an interview broadcast on French television and radio.

Calling the nuclear standoff "the greatest crisis" of present times, the minister said: "We will not accept that the bomb is manufactured," and hinted that military plans were on the way.

In Washington, US Defense Secretary Robert Gates took a more muted approach on Sunday.

"I will tell you that I think the administration believes at this point that continuing to try and deal with the Iranian threat ... through diplomatic and economic means is by far the preferable approach," he said.

The criticism of ElBaradei centers on his cutting a deal with Iran, which says its nuclear work is a peaceful effort to generate electricity, for new nuclear inspections by the IAEA, the verification arm of the Non-Proliferation Treaty (NPT).

Washington fears Tehran will use this as a delaying tactic to avoid facing new UN sanctions for refusing to stop enriching uranium, which can be fuel for civilian power reactors but also the raw material for atom bombs.

At issue is how to win guarantees that Iran's nuclear work is peaceful. US patience is wearing thin as it presses for more UN sanctions but ElBaradei is urging more inspections that could lead to talks on ending the crisis.

In Washington, the US State Department said the six major countries working to resolve the controversy surrounding Iran's nuclear program will discuss a draft UN sanctions text September 21 in the US capital.

The IAEA conference also comes in the wake of an apparent Israeli attack on Syria September 6 that might be related to suspicions that Syria and Iran are buying nuclear material from North Korea.

This new development could envenom what is a regular feature of the IAEA general conference -- an effort by Arab states to get a resolution passed condemning Israel for possessing nuclear weapons.

Israel neither confirms nor denies reports that it has some 200 atom bombs.

Traditionally, a resolution is introduced but then withdrawn and postponed to the following year, in return for Israel agreeing to a call for a nuclear weapons-free zone in the Middle East.

"The Israeli threat resolution will gain more attention this year because of this added issue of Israel once again possibly taking Osirik-type action on a nuclear facility in another country," non-proliferation analyst Mark Fitzpatrick told AFP.

He was referring to Israel's bombing in 1981 of an Iraqi nuclear reactor in Osirik.

Fitzpatrick, a senior researcher at the London-based International Institute for Strategic Studies, said it was not clear if "this attack on Syria was really North Korea related or nuclear related or was it merely a warning to Iran that you are next if you don't suspend your program."

The week-long IAEA conference comes on the 50th anniversary of the watchdog, which was founded in 1957 as the world's "Atoms for Peace" organisation.

The conference includes a scientific forum Tuesday and Wednesday on "Global Challenges and the Development of Atomic Energy: The Next 25 Years."

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