UN atomic watchdog chief Yukiya Amano described Iran Monday as a "special case" in terms of the agency's monitoring, in view of allegations of possible military dimensions to its contested atomic drive.

The West accuses Iran of seeking to build a nuclear bomb, a charge that Tehran vehemently denies.

But after more than seven years of investigation, the International Atomic Energy Agency is still not in a position to state that the Islamic republic's nuclear activities are entirely peaceful.

Iran insists its case should be treated as a routine matter by the IAEA, as is the case with any other member state.

But in his opening address to the agency's 35-member board of governors here, Amano said: "Iran is a special case because, among other things, of the existence of issues related to possible military dimensions to its nuclear programme."

Amano told reporters later that a series of resolutions by the UN Security Council and the IAEA board of governors over the years also meant it was impossible to treat Iran simply like any other member state.

The UN Security Council in New York was meanwhile due to meet later Monday to discuss a package of new nuclear-related sanctions against Iran.

The full 15-member body would consider a draft resolution to impose a fourth round of sanctions on Iran, and was hoping to vote on the text as early as the middle of this week, spokesman Farhan Haq said.

In its latest report on Iran, the IAEA complained that Tehran is pressing ahead with its contested uranium enrichment activities -- despite the three existing rounds of UN sanctions -- and is now producing enriched uranium at even higher levels of purification.

The report said the agency remained concerned about the true nature of Iran's nuclear ambitions.

"Iran has not provided the necessary cooperation to permit the agency to confirm that all nuclear material in Iran is in peaceful activities," Amano told the closed-door session of the board of governors.

Amano also said the IAEA was still waiting for an official response from the United States, France and Russia to Iran's proposed fuel swap deal with Turkey and Brazil.

Amano said he had forwarded the proposed agreement to Washington, Paris and Moscow for their views immediately after receiving it from Iran on May 24.

Diplomats close to the Vienna-based watchdog have said the so-called Vienna group of countries had drawn up a response to Tehran's proposal and were expected to hand it over to Amano imminently.

Under an IAEA-brokered deal last October, the United States, Russia and France had originally proposed taking most of Iran's stockpile of low-enriched uranium (LEU) and turning it into the much-needed fuel for a research reactor in Tehran that makes radioisotopes for medical use.

But Iran refused to take up the offer and has drawn up an alternative deal with Brazil and Turkey instead.

The West has cold-shouldered the arrangement, saying it did not go far enough to allay fears that Tehran is using its nuclear drive as a mask for a covert atomic weapons programme.

Amano noted that the conditions for such a fuel swap had changed since the idea was first tabled in October.

Back in October, Iran's stockpile of LEU amounted to 1,763 kilogrammes. But it has grown since then to 2,427 kilogrammes, meaning the appeal of a fuel swap has diminished for the West, since Iran would be shipping out a much smaller proportion of its overall stock of nuclear material.

Iran had also started enriching uranium to higher levels of purification, despite the West's belief that it does not have the technology to turn that material into the fuel rods of the reactor.

"These are the differences," Amano said. But he insisted it was not up to the IAEA to judge whether the conditions for a deal had deteriorated.

"I need to be impartial," he said. His role was "to facilitate the provision of fuel for the reactor. It's up to the countries concerned" to decide whether a deal could still go ahead under the new altered conditions.

The IAEA's regular June board meeting is scheduled to last all week, with allegations of illicit nuclear work by Syria also on the agenda.

And Arab countries have succeeded in putting Israel on the agenda for the first time since 1991.

Israel is widely believed to have nuclear weapons, but it maintains a policy of refusing to deny or acknowledge its nuclear arsenal.