Iran has agreed to provide early information about any plans to build new nuclear facilities, the head of the UN's nuclear watchdog has said.
Iran says it has nothing to hide
Mohamed ElBaradei welcomed what he said was a greater sign of transparency from Tehran.
Mr ElBaradei discussed Iran's controversial nuclear programme with President Mohammad Khatami in Tehran.
His visit comes amid concern in the United States that Iran's avowed civilian nuclear programme may be a pretext for building nuclear weapons.
President Khatami said his country meant to develop its nuclear industry in line with the Nuclear Non-Proliferation Treaty (NPT) and would further co-operate with the International Atomic Energy Agency (IAEA), to avoid any "misunderstandings".
We hope the Iranian efforts, which are legal and fair, will not become a victim of the discriminatory policies of certain countries
But Mr ElBaradei stressed that Iran could only dispel doubts about its nuclear ambitions by signing up to the IAEA's "additional protocol".
This would allow UN inspectors freer access to nuclear sites with little prior warning.
The protocol was drawn up in 1991 and has only 28 signatories - the US is adopting an amended version of it.
Iran has reportedly refused to allow snap inspections, but the country's top atomic energy official said he was ready to hold more talks on the issue.
Mr ElBaradei met the Iranian leader after visiting a plant now being built near the town of Natanz - a site which Washington suspects could be used to produce fissile uranium for weapons.
Mr ElBaradei ended his visit a day early because he was able to accomplish what he set out to do in one day, his Vienna-based office said.
Two IAEA officials will remain in Iran until Wednesday to visit another nuclear site at Arak.
'Legal and fair'
Mr ElBaradei's visit comes less than a month after Mr Khatami said that Iran had discovered uranium deposits and had started mining near the central city of Yazd.
President Khatami said after his talks with Mr ElBaradei on Saturday that Iran would "continue to co-operate with the IAEA within the rule
of law and allow the agency to inspect and judge its programmes".
First nuclear plant comes online by summer 2004
Has signed up to the
Nuclear Weapons Non-Proliferation Treaty
Can now supply its own power stations with nuclear fuel
"Tehran has signed the NPT and we don't have any restrictions for further talks on various topics," he said, insisting on Iran's
"right to have nuclear technology".
"We hope the Iranian efforts, which are legal and fair, will not become a victim of the discriminatory policies of certain countries," he added.
The US, which last year labelled Iran as part of an "axis of evil", considers the Islamic Republic a state sponsor of terrorism and argues that it does not need nuclear energy in view of its vast existing oil and gas resources.
US State Department spokesman Richard Boucher said Washington had "very grave concerns that Iran is using its supposedly peaceful nuclear programme... as a pretext for advancing a nuclear weapons programme".