U.N. nuclear inspectors are negotiating with Iran for access to as many as four military sites that have programs or equipment that could be diverted to development of nuclear weapons, diplomats at the International Atomic Energy Agency said Thursday.

Speaking on condition of anonymity, the diplomats said the negotiations were sensitive because visits could compromise the secrecy of Iran's conventional military programs. The talks have been underway since June.

The request for expanded inspections comes as the Islamic republic says its patience with the IAEA is running out and it wants an end to intrusive visits. Still, the diplomats said they were confident of striking a deal for access, noting that the Iranians earlier agreed to let inspectors into other military facilities.

Mark Gwozdecky, spokesman for the IAEA, said in a statement that the agency had been "discussing with the Iranian authorities open-source information relating to dual-use equipment and materials which have applications in both the military and in the civilian spheres."

He said the agency had "welcomed Iran's willingness to discuss these topics," but he declined to go into detail.

Iranian negotiator Hoseyn Moussavian said there had been no formal request from the IAEA to visit the facility that is the focus of the agency's interest, the Parchin munitions plant. "They have not asked to see the site, but we are ready to cooperate with the IAEA," he said.

The IAEA has been gathering information about Parchin, a munitions factory and high-explosives test site 20 miles southeast of Tehran, for nearly two years. Nuclear experts say they believe that a building there could be suitable for conducting explosives tests for a nuclear weapons program.

David Albright, a former IAEA inspector and director of the Washington-based Institute for Science and International Security, released commercial satellite imagery of Parchin on Wednesday and said there were grounds for suspicion.

"Based on a review of overhead imagery of this site . . . it is a logical candidate for a nuclear weapons-related site, particularly one involved in researching and developing high explosive components for an implosion-type nuclear weapon," said an institute study by Albright and Corey Hinderstein, a nuclear analyst at the institute.

Iran has been building a large-scale centrifuge system that it says is part of an electric power program, but experts say it could be diverted to enrich uranium for nuclear bombs. IAEA inspectors say that to date they have found no evidence of such a diversion.

Still, after nearly two years of inspections, the IAEA's director, Mohamed ElBaradei, reported earlier this week to board members that the agency still had not grasped the full nature of Iran's efforts.

The Bush administration, which is seeking a tough resolution this week from the IAEA's board, wants to broaden the inspectors' access. An early U.S. draft would grant the IAEA "complete, immediate and unrestricted access" to any site the agency wanted to visit.