The United States and five other world powers said Wednesday they are seeking an "early negotiated solution" to the standoff with Iran over its nuclear ambitions.

US Secretary of State Hillary Clinton and her counterparts from Russia, China, Britain, France and Germany announced the new diplomatic overture to Iran on the sidelines of the UN General Assembly in New York.

Iran has signaled a new willingness to engage the international community over its nuclear program, but has so far failed to meet the terms for talks and its defiance triggered new UN Security Council sanctions in June.

"We agreed to sanctions in June... Now is the time for Iran to engage in real negotiation, in actual constructive dialogue, about its whole nuclear program," British Foreign Secretary William Hague said after the meeting here.

"The unity of the (...six) shows that Iran can't simply walk away from this and refuse to talk about it. The world is not going to forget about this issue," Hague said.

He added he would pass on the message from the six powers to Iranian Foreign Minister Manouchehr Mottaki when he sees him later Wednesday.

In a statement, the six "reaffirmed our determination and commitment to seek an early negotiated solution to the Iranian nuclear issue and focused our discussion on further practical steps to achieve it at an early date."

US officials said there were signs from the Iranians that they may be ready for a meeting in the fall.

A senior US official, speaking on the condition of anonymity, told reporters afterward that the six powers were ready for "such a process, we're committed to a diplomatic resolution and it remains to be seen whether the Iranians are."

The statement read out by EU foreign policy chief Catherine Ashton said the six powers are "ready to engage with Iran" in the context of implementing a nuclear fuel swap deal that was agreed in Geneva in October last year.

It added that they looked forward to an "early meeting" with Iran and were prepared to discuss a "revised arrangement," apparently because Iran has enriched much more uranium in the past year.

Under the deal, Iran would ship most of its low-grade uranium to France and Russia so that it could be enriched further and returned to Iran to fuel a medical research reactor in Tehran.

The deal had been designed to buy time and build confidence while the world community presses Iran to meet its demand to halt uranium enrichment, a program western powers fear masks a drive for a nuclear bomb.

But the deal stalled as Iran sought to modify its terms.

In June, the UN Security Council then approved a fourth round of sanctions against the Islamic republic, which in turn said it would suspend talks until September.

The chief diplomats also "committed themselves" to the full implementation of the new sanctions, the senior US official said.

In Moscow, Russian President Dmitry Medvedev on Wednesday signed a decree banning supplies of S-300 missiles and other arms to Iran, in line with the tougher military and financial sanctions adopted in June.

The United States, which spearheaded the drive for the sanctions, has long argued that Iran will only return to the negotiating table once it feels them bite.

Iran denies US contentions that the Islamic republic is starting to feel the pinch.

The six powers renewed calls for Iran to comply with international demands. Those are that Iran fully open up its nuclear facilities to inspection and halt uranium enrichment.

Iranian President Mahmoud Ahmadinejad, in New York to attend the UN General Assembly meeting, told media that his country was ready to resume talks with world powers over its nuclear program.

The UN sanctions had also damaged the chances for an improvement in US-Iranian relations, he added. He blamed international politics for the growing tensions over the nuclear program.

When asked what would happen if Iran failed to respond to the offer, the senior US official told reporters that engaging Iran directly "is our focus right now."