Iran today intensified its rhetoric in the row over its suspect nuclear programme, responding to a veiled threat of military action by promising to become a "killing field".

The threat came as the international nuclear watchdog opened crucial talks in Vienna on how to dampen Tehran's atomic ambitions.

John Bolton, the hawkish US Ambassador to the United Nations, warned that the republic faced "painful consquences" if it refused to comply. In response, the deputy head of Iran's armed forces retorted: "Iran’s armed forces, through their experience of war, will turn this land into a killing field for any enemy aggressors."

Representatives from the 35 member states gathered at the headquarters of the International Atomic Energy Agency (IAEA) for last-chance talks aimed at defusing the stand-off through diplomatic means.

Oil-rich Iran insists that it only wants to carry out nuclear enrichment activities to produce domestic power, its "God-given right". Much of the rest of the world suspects that the research is a front for a covert weapons programme, by a country which has recently threatened to wipe Israel off the map.

Tehran has been reported to the UN Security Council and diplomats are meeting this week to agree on carrot-and-stick measures designed to bring the regime back into line. Iran yesterday raised the stakes by vowing that it would scale up its research operations into large-scale uranium enrichment if it was unhappy with the outcome.

Mohamed ElBaradei, who leads the UN's nuclear watchdog body, opened the week of talks by saying that he remained hopeful a deal could be reached. He said that there was frantic diplomatic activity to try to get Tehran and the European Union back to the negotiating table.

"The sticking point remains the question of the centrifuge-related research and development," he told reporters before the meeting began. "That issue is still again being discussed this week and I’m still very much hopeful that in the next week or so an agreement could be reached."

He said that a deal on small-scale enrichment - which Iran resumed last month - and a resumption of talks between Tehran and the EU3, comprising England, Germany and France, would be enough to head off immediate Security Council action.

Last-ditch negotiations over a compromise proposal, under which uranium would be enriched for Iran by Russia, broke up without agreement on Friday.

"There has been lots of progress on many elements of that agreement. I think there is agreement that industrial-scale enrichment should be suspended," he said.

He said that Iran was cooperating with inspectors, "but not with the magnitude and the speed expected".

Ali-Asghar Soltanieh, Iran’s ambassador to the IAEA, reiterated Tehran’s defiance. "We will not show any flexibility on research and development," he told AFP in Vienna.

The IAEA board reported Iran to the Security Council on February 4 but left a month open for diplomacy until the world body gets ElBaradei’s report.

The board is widely expected to set Iran a new 30-day deadline by which it must halt the nuclear programme and comply with international inspectors, or face being referred to the Security Council for further action.

Both the US and the EU3 are thought to favour sanctions targeted on Iran’s nuclear programme and the clerical elite behind the regime. This could include a ban on its 100 top leaders travelling outside Iran, as well as freezing their bank accounts. There is also talk of soft sanctions, such as banning the football-mad nation's team from entering the World Cup.

As the IAEA met in Vienna Condoleezza Rice, the US Secretary of State, was holding simultaneous talks in Washington with Sergei Lavrov, the Russian Foreign Minister.

Russia and China, both of which are permanent members of the UN Security Council, are reluctant to authorise even limited sanctions.

Time magazine reported that the US will show to the Security Council diagrams from a computer, stolen from an Iranian nuclear engineer and obtained by the CIA in 2004, that are believed to depict an atomic bomb.

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