Iran believes the conditions have been met to sign an additional protocol to the nuclear Non-Proliferation Treaty (NPT) as demanded by the UN atomic watchdog, the state news agency IRNA said.
The report came shortly before the start of a joint visit to Tehran by the foreign ministers of Britain, France and Germany, an initiative which IRNA said would accelerate the signing of the protocol.
"Taking into account the positive results and the accord obtained between the IAEA and Iran ..., the conditions for the signature of the additional protocol have now been met," it said, quoting "a well-informed source".
It said Foreign Secretary Jack Straw of Britain, France's Dominique de Villepin and Germany's Joschka Fischer on their mission would "assure Iran that they will assist Iran's peaceful, civil nuclear programme".
"The presence of the three foreign ministers will have a determining role in accelerating this process," IRNA said amid mounting signs that Tehran may bow to demands it open up its suspect nuclear programme to tougher scrutiny.
Fischer was the first to arrive in Tehran at the start of the European Union mission to receive assurances from the Islamic republic it will cooperate with the International Atomic Energy Agency (IAEA).
Asked if he was confident of a deal on the nuclear standoff, the German foreign minister said: "I hope so. We shall have talks and I hope the talks will be successful.
"We hope we will have productive and constructive discussions. These are very serious issues," Fischer, who was greeted at the airport by Iranian foreign ministry officials, told journalists.
The ministers were to hold talks here Tuesday, just 10 days before the expiration of an IAEA deadline for Iran to come clean on its nuclear activities.
Iran's representative to the nuclear watchdog, Ali Akbar Salehi, meanwhile, said that two days of "intensive" talks with IAEA experts had yielded an "understanding" on reinforced inspections.
"We found a mutual understanding," he told AFP.
He said Iran "now has a more positive stance" towards signing the additional protocol which would give the green light to the IAEA to carry out surprise inspections of suspect facilities.
Salehi said it was now up to the Iranian leadership to make a final decision.
The IAEA decided in September to set an October 31 deadline for Tehran to allow tougher inspections of its nuclear programme and answer widespread fears it may be secretly developing atomic arms.
Salehi said Tehran would also satisfy the IAEA's demands for answers to a number of "outstanding issues" -- or serious questions sparked by the discovery in Iran of highly enriched uranium by IAEA inspectors.
Signs of a breakthrough in the often bitter stand-off were coupled with Britain, France and Germany taking the cover off a frantic and secretive diplomatic bid aimed at defusing the crisis peacefully.
Diplomats say the EU's big three have for months been engaged in an effort to convince Iran to fully comply with IAEA demands, and say they were unlikely to launch such a high-profile mission unless they were certain of some success.
Iranian officials said the foreign ministers would be meeting with President Mohammad Khatami.
While the German foreign ministry said the three would "make clear" concern over Iran's nuclear programme, the French set the tone of high expectations by noting "the Iranian authorities now seem prepared to announce a certain number of confidence-building measures aimed at the international community."
In return for Iranian compliance, the three are believed to have offered technical assistance, and possibly supplies of nuclear fuel in order to satisfy Iran's desire for nuclear power while keeping the sensitive nuclear fuel cycle -- and the risks to proliferation it entails -- out of the country.
Iran denies it is developing nuclear weapons.
But the IAEA says its inspectors need the extra powers granted by the extra protocol to fully verify and accurately report on a nuclear energy programme that Washington suspects is a cover for a drive to acquire an atomic bomb.