Updated

The U.N. nuclear agency chief will fly to Tehran over the weekend to sign a deal meant to allow his organization to resume probing Iran's disputed nuclear program, the agency and diplomats said Friday.

An International Atomic Energy Agency statement announcing the Sunday trip said only that Yukiya Amano would "discuss issues of mutual interest with high Iranian officials" during his one-day visit, which will include a meeting with Iran's chief nuclear negotiator, Saeed Jalili.

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.

Iran insists its nuclear program is peaceful, but the U.S. and others doubt its sincerity.

Iranian officials are to meet with delegates from the U.S. and five other world powers in Baghdad on Wednesday. Washington in particular hopes to wrest nuclear concessions from Tehran aimed at reducing fears it seeks to develop atomic arms.

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, which can quickly be turned into fissile warhead material.