According to IAEA officials, Iran's suspension of nuclear construction is part of a demand that the agency conclude its investigation into the country's nuclear activities at its next board meeting in June.

In the meantime, IAEA spokesman Mark Gwozdecky, who is in Tehran with Mr. ElBaradei, says Iran promised to improve its cooperation with the agency's inspectors.

"He has had one meeting so far with Aghazadeh, who is president of the Atomic Energy Organization of Iran," he said. "The two things that ElBaradei mentioned was that Iran has agreed to accelerate its cooperation with the agency and we will have a team of inspectors that will begin work here on April 12."

At the June meeting, the 35-nation IAEA Board of Governors is scheduled to discuss whether the Iran file should go to the U.N. Security Council for possible sanctions.

Last month the Board passed a strong resolution deploring Iran's concealment of its nuclear activities. The board called for an explanation of sensitive nuclear experiments and the origin of contamination from highly enriched uranium discovered by inspectors at two locations.

In response, Iran delayed inspections and threatened to break off co-operation with the IAEA.

Iran has signed an additional protocol to the Nuclear Non-Proliferation Treaty that gives international inspectors the authority to visit nuclear related facilities at short notice.

The United States and other countries continue to believe that Iran is secretly working on a nuclear weapons program, something the Iranian government strongly denies.