Iran angrily stayed away Monday from a UN atomic agency forum on creating a Middle East free of nuclear weapons that saw Israel under fire from Arab nations for its alleged possession of the bomb.

Iran's ambassador to the Vienna-based International Atomic Energy Agency, Ali Asghar Soltanieh, said Tehran's decision was its "first reaction" to the body's "inappropriate" recent report on its nuclear programme.

That assessment saw the IAEA come the closest yet to accusing Iran outright of seeking to develop nuclear weapons. Iran, hit by four rounds of UN sanctions, says its activities are exclusively for peaceful purposes.

On Friday, the IAEA's board of governors passed a resolution of "deep and increasing concern" submitted by the five permanent members of the UN Security Council, Germany and 12 others in light of the report.

Soltanieh said another reason for not attending the two-day IAEA forum, aimed at learning from the experiences of other so-called nuclear-weapon-free zones (NWFZ), was Israel's unofficial atomic arsenal.

"As long as the Zionist regime does not belong to the NPT (nuclear non-proliferation treaty) ... this kind of conference is useless and cannot succeed," Soltanieh told Iranian television channel Al-Alam.

Israel is widely believed to possess nuclear weapons but has never confirmed it. Unlike Iran it is not a signatory to the NPT and therefore not subject to IAEA inspections.

Syria, reported by the IAEA to the Security Council over a suspected covert reactor allegedly bombed by Israel in 2007, was however present at the forum, along with Israel, 17 other Middle East states and Palestinian representatives.

Some of the roughly 275 participants from 97 countries in the closed-door discussion said representatives of several Arab states, particularly Syria and Lebanon, had used their speeches to attack Israel.

"Israeli nuclear capabilities pose a grave and continuous threat to others in the region. Israel must join the NPT," Syria's ambassador Bassam Sabbagh said, according to one participant.

But David Danieli, deputy head of Israel's Atomic Energy Commission, said that a process towards a nuclear-free Middle East "can only be launched when normal peaceful relations exist in the region," according to a participant.

Danieli said that vital pre-requisites were still absent, most notably mutual recognition -- very few countries in the region have diplomatic relations with Israel -- "and an atmosphere conducive to direct negotiation."

Germany's ambassador Ruediger Luedeking agreed: "Recognition is the minimum requirement."

Participants said the atmosphere was however less "confrontational" than previous IAEA events that have degenerated into Arab-Israeli slanging matches, most notably the annual conferences of the agency's roughly 150 member states.

NWFZ treaties prohibit the production, acquisition and stationing of nuclear weapons, as well as nuclear testing.

Zones of this kind already exist in Latin America and the Caribbean, the South Pacific, Southeast Asia, Africa and Central Asia, encompassing 113 countries.

IAEA member states requested in 2000 that such a Mideast forum take place but agreement on holding such a meeting remained elusive until now.

The forum comes ahead of a conference to be hosted by Finland next year on ridding the powder keg region, rocked this year by Arab Spring popular uprisings in several countries, of nuclear weapons.

IAEA head Yukiya Amano, opening the forum, conceded there were "long-standing differences of view" on creating such a zone.

"It has taken 11 years to get to this point," Amano said. "I hope it will nurture fresh thinking -- creative thinking."

"It's up to Iran to consider if it can make a contribution. Clearly they felt not," South Africa's IAEA ambassador Abdul Samad Minty told reporters.

"But this (the forum) is a first step. It's not the end of the process."