Chief U.N. nuclear inspector Mohamed ElBaradei will fly to Iran this week, his spokeswoman said Monday, in a visit that will overlap with U.S. President George W Bush's Middle East tour. Diplomats, meanwhile, said Tehran has started sharing information about past programs the U.S. says were attempts to make atomic arms.

As head of the International Atomic Energy Agency, ElBaradei has spearheaded more than four years of international efforts to press Iran for full disclosure of its nuclear activities. ElBaradei spokeswoman Melissa Fleming said he would visit Tehran Friday and Saturday "with a view of resolving all remaining outstanding issues and enabling the agency to provide assurance about Iran's past and present activities."

She said ElBaradei would "meet with a number of high officials" but provided no other details in an e-mailed statement. A diplomat familiar with ElBaradei's itinerary who demanded anonymity because the information was confidential said, however, that the nuclear chief expected to meet with supreme leader Ayatollah Ali Khamenei and President Mahmoud Ahmadinejad.

The trip comes at a time of renewed U.S. efforts to keep the pressure on Iran on the nuclear front.

While meeting the leaders of Israel, Egypt, Saudi Arabia and other regional nations Jan. 9-16, Bush is expected to try to bolster the troubled peace process between Israel and the Palestinians. He is also likely to seek backing for U.S. concerns about Tehran's refusal to cease uranium enrichment and other activities that could be ultimately used to make nuclear arms.

A recent U.S. intelligence assessment that Iran had a clandestine weapons program but stopped working on it four years ago has hurt Washington's attempts to have the U.N. Security Council impose a third set of sanctions on Tehran for failing to mothball enrichment.

While low enriched uranium can be used as nuclear fuel, high-level enrichment creates the fissile material used in nuclear warheads. Tehran says it never worked on atomic weapons and wants to enrich only to generate electricity. The U.S. and its allies say that — even if Iran no longer has an active weapons program — it can return to it, and then use its enrichment program to tip its missiles with nuclear payloads.

Ahead of the Bush visit, an Israeli defense ministry official said the Jewish state will urge him to reassess the U.S. conclusion that Iran stopped its active nuclear weapons development in 2003.

Defense Minister Ehud Barak will tell Bush that Israeli intelligence analysts conclude that Iran is continuing to try to produce nuclear arms, the official told the AP. He asked for anonymity because he was barred from publicly commenting on the talks in advance.

Part of past evidence presented by the U.S. to close allies and the IAEA to back its allegations was material on a laptop computer reportedly smuggled out of Iran. In 2005, U.S. intelligence assessed that information as indicating that Tehran had been working details of nuclear weapons, including missile trajectories and ideal altitudes for exploding warheads.

U.S. intelligence was also shared with the agency on the "Green Salt Project" — a plan that the U.S. alleges links diverse components of a nuclear weapons program, including uranium enrichment, high explosives testing and a missile re-entry vehicle.

The IAEA is also interested in activities a former research center at Lavizan-Shian, which Iran razed before allowing agency inspectors access. The center is believed to have been the repository of equipment bought by the Iranian military that could be used in a nuclear weapons program.

Iran has long dismissed such claims as U.S. propaganda and refused to talk about them. But on Monday, diplomats familiar with the Iran file told The Associated Press that Tehran had started substantial discussions with agency experts on at least some of the issues linked to "weaponization," as part of an IAEA probe of Tehran's past nuclear activities launched last year.

"Talks have already begun," said one of the diplomats. "But they could take a couple of months."

ElBaradei had said he wanted to wrap up the investigation by December. But a diplomat accredited to the agency recently told the AP that Iranian officials were now talking about March as the new deadline.

The U.S. and its allies are likely to be unhappy with such a delay but would have little choice other than to wait if ElBaradei can show progress on clearing up the most sensitive blank spots in Iran's nuclear record.

Under the plan, Iran committed itself to answering all lingering questions about its past nuclear activities — including those it has evaded since 2003, when nearly 20 years of clandestine atomic work on the part of Tehran were revealed.

Publicly, the agency has been careful about the progress of its probe.

In an August report, ElBaradei said the agency felt that information provided by Iran on past small-scale plutonium experiments had "resolved" agency concerns about the issue. It has also confirmed that Tehran has given agency experts a copy of documents showing how to form uranium metal into the spherical shape of warheads.

But it specified that Iran still needed to satisfy the agency's curiosity about the issues that are potentially more important in determining whether the country has or had a military program — among them, the "Green Salt" project, the history and present state of its enrichment technology and the origins of traces of highly enriched uranium at a facility linked to the military.