The head of the UN's atomic watchdog agency said last night that he had "useful" and "intensive" negotiations in Tehran that would have "positive effect" on Iran's high-stakes nuclear talks with six world powers in Baghdad tomorrow, Iranian media reported.
But it was far from clear whether Yukiya Amano, on his first visit to Iran, had clinched a key agreement for Tehran to address concerns about "possible military dimensions" to its nuclear programme.
That would require that Iran provide access to scientists, sensitive documents and, most importantly, a suspect military complex outside Tehran at Parchin - demands that Iran had rejected for four years.
Mr Amano, the director general of the International Atomic Energy Agency (IAEA), declined to address that issue but indicated there were still differences. "I will not go into details, but the agency has some viewpoints and Iran has its own specific viewpoints," he said.
Iranian officials did not permit foreign journalists to approach Mr Amano, so it was impossible to independently verify his comments.
Iran, seeking relief from increasingly punitive sanctions targeting its vital oil sector, will hope its cooperation with Mr Amano, however limited, will strengthen its hand in tomorrow's negotiations with representatives from six world powers. They are the five permanent members of the UN Security Council - the United States, Britain, China, France and Russia - and Germany, a coalition called the P5+1.
The IAEA has long sought explanations for intelligence information, described as "credible" in a report by the agency last November, pointing to research on the design and testing of nuclear warheads until 2003 and possibly beyond.
Iran insists the "childish" and "ridiculous" allegations are based on "fabricated documents" provided by hostile spy agencies, but it recently signalled it was ready to address the issue, declaring it has nothing to hide.
Even if, despite repeated denials, Iran conducted weapons research in a special metal chamber at Parchin, it would be most unlikely to admit it without firm guarantees that it will not be slapped with further sanctions, analysts said.
Any deal with the IAEA in itself is not enough to allay international concerns. The six world powers want Iran to curb uranium enrichment, which can have both civilian and military purposes. That will be the focus of the Baghdad talks.
The West's immediate aim is to get Iran to relinquish its enrichment of uranium to 20 per cent, which is a short technological step for producing bomb-grade material. Iran says it is only purifying to this level to fuel a research reactor providing medical isotopes for cancer patients.
Iran insists its nuclear programme is solely peaceful and that, as a signatory to the nuclear Non-Proliferation Treaty, it has the right to enrich uranium for civilian purposes.
The US seemingly accepts that Iran will never relinquish its domestic nuclear fuel cycle, in particular its enrichment to 3.5 per cent, the level required to fuel electricity-generating nuclear reactors.
So Iran's negotiations with the P5+1 are likely to focus on the scale and level of enrichment that the West might accept, along with the timing and extent of reciprocal concessions on the sanctions.
The spectre of military action against Iran by the US or Israel - the sole if undeclared nuclear weapons state in the Middle East - looms should the nuclear talks fail to make headway.