A high-level team from the United Nations' nuclear watchdog said yesterday it had held "good talks" in Tehran and planned another visit later this month.
The announcement indicated progress was made in persuading Iran to address suspicions that its nuclear programme has a military dimension.
If so, that could defuse tensions that have escalated to crisis level in recent weeks. The US is beefing up its naval muscle in the Gulf while Iran is planning new military exercises there this month amid a war of nerves over the Strait of Hormuz, a key oil trade route.
"We are committed to resolving all outstanding issues and the Iranians said they are committed too," said Herman Nackaerts, who led the six-man team from the International Atomic Energy Agency (IAEA) on a three-day mission to Tehran.
Sounding cautious but upbeat on his return to Vienna, where the IAEA is based, he said: "There's still a lot of work to be done, so we have planned another trip in the very near future."
Iran, keen to show goodwill in the battle for public opinion, hailed the talks as "constructive".
The UN secretary general, Ban Ki-moon, yesterday bluntly told Israel, which has repeatedly threatened to use force to cripple Iran's nuclear programme, that the dispute must be resolved peacefully.
Sanctions and diplomacy could yet persuade Iran to give up any ambitions it may have to weaponise its nuclear programme, the head of US intelligence said on Tuesday. "We judge Iran's nuclear decision-making is guided by a cost-benefit approach, which offers the international community opportunities to influence Iran," James Clapper told Congress.
He implicitly countered alarmist talk by hawks in Israel and Washington that Iran is determined on the bomb and on the verge of acquiring one.
"We assess that Iran is keeping open the option to develop nuclear weapons, in part by developing various nuclear capabilities that better position it to develop such weapons, should it choose to do so," he said. "We do not know, however, if Iran will eventually decide to build nuclear weapons."
Combined US and European sanctions will "weigh down" the Iranian economy, yet these difficulties "probably will not jepoardise the regime, absent a sudden and sustained fall in oil prices or a sudden domestic crisis that disrupts oil prices," Mr Clapper said.
Bolstering Iran's position are assurances from India and China, major buyers of Iranian oil, that they will not cut back on imports from the Islamic republic, despite US pressure.
Most western media, however, chose to focus instead on Mr Clapper's warning that there is an increasing likelihood that Iran could carry out terrorist attacks on American soil and allied targets around the world.
He said an alleged plot to assassinate the Saudi ambassador in Washington last year "shows that some Iranian officials - probably including the supreme leader, Ali Khamenei - have changed their calculus and are now more willing to conduct an attack on the United States in response to real or perceived US actions that threaten the regime."
The IAEA team visited Iran to seek explanations for evidence, described as "credible" in a report by the UN nuclear agency in November, pointing to past experimentation on nuclear weapons design.
That report was followed by unprecedently tough US and European Union sanctions targeting Iran's vital oil exports.
Iran, which insists its nuclear programme is solely peaceful in nature, has refused to discuss the alleged weapons experiments for more than three years, saying they are based on "fabricated documents" provided by hostile intelligence agencies.
The IAEA report confirmed the agency had detected no diversion of nuclear material for military purposes and that it maintains a strict inspections watch over Iran's known nuclear facilities.
Leon Panetta, the US defence secretary, said this month Iran could develop a nuclear weapon in a year if it chose to do so, but it could take another two for Tehran to have a missile delivery vehicle for such a bomb.
That allows time for a diplomatic solution, but many analysts are pessimistic. It is election year in the US and, facing strident Republican charges of being weak on Iran and insensitive to Israeli concerns, Barack
Obama, the US president, may well be reluctant to ease sanctions even if Iran offers concessions.
Decision-making in Iran is equally paralysed by fears of looking soft on the "global arrogance" of America.