The U.N. nuclear agency chief will fly to Tehran over the weekend to sign a deal meant to allow his organization to resume a long- stalled search for evidence that Iran worked on developing nuclear arms, the agency and diplomats said Friday.

The trip Sunday by International Atomic Energy Agency chief Yukiya Amano comes just four days ahead of a key meeting between six world powers and Iran where the six hope to wrest concessions from Tehran meant to reduce concerns that it wants such arms.

An IAEA statement announcing the Sunday trip said only that Amano would "discuss issues of mutual interest with high Iranian officials" during his one-day visit, which will include a meeting with Saeed Jalili. Iran's chief nuclear negotiator will also represent his country at the meeting Wednesday in Baghdad with the six world powers.

But diplomats said the visit was scheduled to allow both sides to agree on an accord outlining the mechanics of IAEA access to sites, information and officials it seeks for its investigation into whether Tehran secretly conducted nuclear weapons research and development.

The diplomats demanded anonymity because their information was confidential. They cautioned that signing such a deal was only the first step, adding that its implementation was the true test of Iranian willingness to end more than four years of refusing to work with the IAEA probe after some initial cooperation.

Still, if Iran does abide by such a deal and give the IAEA the access it seeks, that could result in putting to rest the dispute over whether the Islamic Republic hid such work from the rest of the world. A second round of talks on the issue had been scheduled in Vienna after and Iran-IAEA meeting last week in the Austrian capital, and the surprise announcement that Amano would instead be flying to Tehran strongly suggested that a deal was ready to be signed.

Iran agreed to answer questions on the allegations in August 2007, but after several months of cooperation declared the issue closed, saying it had fulfilled its commitments and accusing the agency of going beyond its mandate in pushing for more information. Since then, Iran has blocked the IAEA investigation, insisting its nuclear program is peaceful.

Tehran could point to any deal reached with Amano as proof of its willingness to compromise and demand that the six — the United States, Russia, China, Britain, France and Germany — in return temper demands that Iran end higher-level enrichment of uranium.

Iran says it is enriching only to create nuclear fuel, but its critics fear it will use the technology to arm warheads. Its refusal to halt enrichment has provoked U.N. and other sanctions, including U.S. and European Union penalties meant to cripple its oil exports — its main revenue source — that are to fully take effect in a few weeks.

While the six powers publicly continue to insist that Iran heed U.N. Security Council demands and stop all enrichment, diplomats have said they now are ready to accept Tehran's right to make low-enriched uranium for energy if it stops producing uranium enriched to higher levels of 20 percent, which could be turned quickly into fissile warhead material.

Allegations of secret work on developing nuclear weapons have compounded concerns over Iran's enrichment activities, with the IAEA saying for the first time in November that Iran is suspected of conducting secret experiments whose sole purpose is the development of nuclear arms.

In a report, it outlined suspected Iranian work on high-explosives testing and detonator development to set off a nuclear charge, as well as computer modeling of a core of a nuclear warhead. It also cited apparent preparatory work for a nuclear weapons test, and development of a nuclear payload for Iran's Shahab 3 intermediate range missile — a weapon that can reach Israel.

Some of the information was new, including evidence of a large metal chamber at Iran's Parchin military site for nuclear-related explosives testing. Diplomats in recent weeks have said that satellite photos show an apparent clean-up at that site, ahead of any possible IAEA visit — a charge Iran denies.


Associated Press writer Juergen Baetz in Berlin contributed.