At an EU ministerial meeting in Brussels, he said that negotiators from Iran and the foreign ministers of Britain, France and Germany, plus EU foreign policy head Javier Solana would meet in Geneva on Wednesday.

"The issue before us will be to ensure that both sides stick by the agreements which we have already entered into," Straw said, referring to pledges to suspend key nuclear enrichment activities made in November.

Of the crisis talks he said: "I think they will be tough, but I think very much they will be successful."

As if on cue, a senior Iranian official said the negotiations were likely to be the last chance for the two sides.

"We would reach the conclusion that we haven't got along with them," if they fail, Ali Agha Mohammadi, the spokesman for Iran's Supreme National Security Council, told the student news agency ISNA.

He said the Iranians may not even travel to Geneva if no satisfactory offer is made during talks between experts in Brussels, scheduled for Tuesday.

Whether it was brinkmanship, rhetoric for public consumption ahead of next month's presidential election or a statement of fact, Solana refused to be drawn and said only that he was hopeful.

"I would prefer not to develop further at this point in time," he said. "I hope that the meeting will take place in Geneva."

Iran is suspected by the United States of wanting to build atomic weapons.

But the Islamic republic insists it has the right to master the full nuclear fuel cycle, including enriching uranium, as a signatory of the nuclear Non-Proliferation Treaty (NPT) and that it only wants to generate electricity.

Iran agreed in November not to resume uranium conversion; a precursor to the ultra-sensitive enrichment process which has prompted fears of a secret weapons programme, but has indicated it may end that suspension.

"The Iranians are tough to negotiate with, but so far the Iranians have accepted, as we, that it is in the interest of Iran, Europe and the international community that we should reach agreement," Straw said.

He declined to be drawn on what proposals the EU side would make, though it is believed to be ready to compromise on fuel supply for Iran's reactors and to offer trade incentives.

In other developments, the EU called on Uzbekistan to reconsider its refusal to allow an independent probe into the killings in the east of the country, warning that otherwise it could take "further steps."

Witnesses, rights groups and opposition activists say the military crackdown that began on May 13 involved the indiscriminate slaughter of as many as 1,000 people in Andijan and neighboring towns.

Karimov, who acknowledges that almost 200 people died but refuses a probe, claims his forces deployed in response to an attempt by dozens of armed Islamic extremists supported by local residents to overthrow the government.

Meanwhile, the EU's Luxembourg presidency said the Union would be plunged into crisis if French voters reject the new constitution on Sunday.

"We will enter a big crisis. There is no easy way out, and that is what Europe doesn't really need now," junior Luxembourg foreign minister Nicolas Schmit told reporters.

Two recent opinion polls gave the "no" camp 52 percent, against 48 percent for supporters of the treaty.

All rights reserved. © 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.