Iranian leader Mahmoud Ahmadinejad plans to join a major UN nuclear disarmament summit next week in New York, even as the US and other powers seek tougher sanctions at the world body to halt Tehran's suspect atomic work.

Iran's UN mission said president Ahmadinejad applied Wednesday for a US visa to lead Iran's delegation to the non-proliferation treaty (NPT) review conference opening Monday at the United Nations headquarters.

US Secretary of State Hillary Clinton will be among more than 30 foreign ministers who will attend the opening of the conference, which is held every five years to check compliance with the arms control treaty.

Officials said they expected Ahmadinejad to be granted the visa but doubted Clinton would hold one-on-one talks with the leader of a country that Washington suspects of pursuing a covert nuclear weapons program.

Iran denies the charge, saying it seeks peaceful uses of nuclear energy.

Clinton said Tuesday that "nothing new" came from Iran's weekend talks with the International Atomic Energy Agency (IAEA), the UN's nuclear watchdog, which has seen Tehran balk at a confidence-building proposal to swap nuclear fuel.

Clinton's spokesman Philip Crowley urged Iran to play a "constructive role" in the conference, but added it "wouldn't surprise us" if Tehran acts much the way it has in defying international demands to halt its sensitive nuclear work.

In that case, he warned, Iran's leadership will face "further isolation".

The United States is spearheading a drive for a fourth set of UN Security Council sanctions -- sanctions Clinton hopes will be "crippling" -- against Iran over its refusal to curb uranium enrichment.

However, Washington has seen negotiations for a new sanctions resolution drag out as it struggles to persuade reluctant Security Council member countries like China, Brazil, Turkey and Lebanon to adopt biting sanctions.

Susan Rice, US President Barack Obama's ambassador to the United Nations, first broke the news that Ahmadinejad had applied for a US visa.

"Iran is obviously in any case in the backdrop when consideration of the non-proliferation treaty is occurring because it remains in violation of its obligations," she told reporters in New York.

"But we think this is much bigger than any one country, and our aims are universal and we approach it in that vein," she added.

Rice said that the United States, Britain, China, France, Russia and Germany were pursuing "intensive" negotiations over new UN sanctions against Iran.

But analysts said that if Ahmadinejad attends the meeting he was likely to reaffirm that Iran, which signed the NPT, does not seek a nuclear weapons capability.

Instead he was likely to turn the spotlight on arch-enemy Israel, which is widely believed to have an arsenal of several hundred nuclear bombs.

Israel has never publicly acknowledged having nuclear weapons, maintaining a policy of deliberate ambiguity since it inaugurated its Dimona nuclear reactor in 1965.

Like nuclear-armed countries India, Pakistan and North Korea, the Jewish state is not party to the treaty in order to avoid international inspections.

Crowley said Ahmadinejad's visa application was received earlier on Wednesday via Switzerland, which represents US interests in Iran in the absence of diplomatic ties between the two countries for more than 30 years.

With its obligations as the United Nations host, the United States will not "stand in the way" if the Iranian leader wants to travel to New York to lead his delegation to the conference, Crowley said.

Iranian official Mohammed Baksahraee told AFP from Iran's permanent mission to the United Nations in New York that Ahmadinejad "is expected to attend the (NPT) meeting," and would head Iran's delegation.