UN nuclear watchdog chief Mohammed ElBaradei has said he is cautiously optimistic that Iran will meet the deadline set by the agency to prove that it is not trying to produce nuclear weapons.
By Jim Muir
BBC Tehran correspondent
Mr ElBaradei, who heads the International Atomic Energy Agency (IAEA), told the BBC that he had been informed that in the next few days Iran would be providing the agency with all the information it needs to answer many outstanding questions.
But he added that he could not compromise on the 31 October deadline, even if that meant Iran had to make certain admissions.
"It's in the interests of Iran to come clean and... to admit everything for us to take the corrective action necessary and to demonstrate that everything is on board, under safeguard," Mr ElBaradei said in Tehran.
He said he was also optimistic that Teheran would sign an additional protocol which would allow the IAEA to conduct tougher inspections in the future.
In that regard, envoys from three European countries - Britain, France and Germany - have made low-profile visits to Teheran this week.
They offered to help ensure that Iran does have access to nuclear fuel under safeguards if it satisfies the IAEA's requirements.
Mr ElBaradei was asked by the Iranians to come to Teheran at this crucial moment, with just two weeks to go before the deadline expires.
He said he believed the Iranian leadership had taken a clear decision to put the past behind it.
He said that once a decision had been made to provide all the necessary information, it should not take much more than a week, although the IAEA would then need some more time to verify what it had been told.
Mr ElBaradei said he was cautiously optimistic that Iran would move in the direction the international community wanted.
So, Mr ElBaradei's short visit to Tehran is ending on a hopeful note, but everything will depend now on Iran co-operating fully, as it said it will do, in the next two weeks.