Iran has turned over a long-withheld blueprint showing how to mould uranium metal into spheres for nuclear warheads, meeting a demand of U.N. investigators ahead of a watchdog report, diplomats said.
But some diplomats said while the report was likely to say Iran has improved cooperation with a long-running inquiry into its nuclear programme, this might not yet be enough to resolve any key questions about the scope and nature of the effort.
The timing and toughness of any further U.N. sanctions against Iran will hinge on world powers' interpretation of the International Atomic Energy Agency report and a parallel report by the EU's top diplomat on recent dialogue with Tehran.
Diplomats have little doubt the European Union's Javier Solana will confirm that Iran remains unwilling to suspend uranium enrichment, which Iran says is to generate electricity but the West suspects is to make atom bombs.
Tehran's continued defiance of U.N. Security Council demands to stop enrichment alone would trigger moves to wider sanctions in the view of the United States, Britain, France and Germany, citing a game plan agreed in September with Russia and China.
A senior diplomat close to the IAEA said a top Iranian nuclear official turned over the uranium metals document at a meeting in the agency's headquarters in Vienna last week.
IAEA inspectors came upon the document accidentally in 2005 while examining Iranian nuclear facilities suspected to have military dimensions. Iran had allowed inspectors to look at but not make copies of the document for investigative purposes.
Iran has said it received the blueprint unsolicited from the former nuclear smuggling network of Pakistan's A.Q. Khan, which laid the groundwork for Iran's programme, but did nothing with it. IAEA experts have said the document's instructions could have uses other than in a quest for nuclear weapons.
Iran's concession on the metals blueprint highlighted what diplomats accredited to the IAEA said were some signs of Iranian transparency as the agency put finishing touches on its report, due to be issued on Wednesday or Thursday.
"(But while) we may well see some clear cooperation from Iran but it's unclear whether it will be enough to actually move forward in the 'work plan'," one diplomat said, referring to IAEA questions Tehran promised in August to resolve one by one.
Still, any new show of Iranian cooperation could spur Russia and China to persist in delaying harsh sanctions at the Security Council. They could argue for more time for the IAEA process to reach fruition and against steps to isolate Tehran which they regard as a slippery slope to war.
Iran said on November 3 it gave the IAEA all information needed to remove ambiguities about the first major question on the list -- the extent of work to develop centrifuges which enrich uranium -- and there would be no more discussions about it.
Diplomats said there were indications Iran had turned over centrifuge documentation that was withheld for years, among various indications of efforts to militarize the programme.
It was unclear, they said, whether Iran had granted the IAEA long-sought interviews with certain nuclear programme leaders believed to have had military links, or visits to workshops developing a high-performance centrifuge known as the P-2.
Both steps would be key to closing the centrifuge file. Iran so far has been refining uranium with an old, erratic P-1 model.
"Whether everything was put on the table (by Iran) that needs to be there remains to be seen," said an EU diplomat.