The head of Iran's national security council is to travel to Vienna for a meeting on Saturday with the head of the International Atomic Energy Agency (IAEA), Mohammed ElBaradei.
By Jim Muir
BBC Tehran correspondent
An announcement from the agency said the Iranian official, Hasan Rohani, would be handing over a letter connected with Iran's nuclear programme.
Mr ElBaradei is in the process of preparing a report on Iran's nuclear activities for the IAEA's board of governors, which meets on 20 November.
Mr ElBaradei is preparing a report on Iran's nuclear activities
Iran has already handed over a thick file of documents on questions raised by the agency about its past nuclear activities.
Inspectors are busy in Iran now trying to verify the information they have been given, but that process may have to go on for some months.
It is not clear whether Mr Rohani's mission is to provide further clarification at this stage, but he is to hand over a formal letter.
That may well turn out to be the "letter of intent" that the IAEA is expecting to receive from Iran in the next few days, serving formal notice of its intention to sign the additional protocol with the IAEA.
That would permit tougher international inspections - a step Iran has announced it is ready to take. It has also said it is ready to suspend its uranium enrichment activities, though it has not done so yet.
Iran hopes that all that, plus the revelations included in its account of its past nuclear activities, should be enough to ensure that the IAEA board meeting resists US pressures to have Iran referred to the UN Security Council for breaching its obligations under the non-proliferation treaty.