The U.N. nuclear watchdog agency is pushing for a fresh look at an Iranian military complex linked by the United States to possible atomic arms research just days after being granted limited access, diplomats said Tuesday.

The International Atomic Energy Agency (search) is interested in testing another part of the sprawling Parchin complex (search) just outside Tehran in its search for radiation that could point to such research, the diplomats said.

The Bush administration has accused Iran of being part of an "axis of evil" with North Korea and prewar Iraq. The United States alleges Iran may be testing high-explosive components for nuclear weapons, using an inert core of depleted uranium at Parchin as a dry run for a bomb that would use fissile material.

The request by the Vienna-based IAEA comes just days after its inspectors were given partial access to the site and were allowed to take environmental samples for analysis in the agency's European laboratories.

The diplomats, who are familiar with the agency's investigation of Iran's nuclear programs, said that as far as they knew the IAEA experts were not impeded beyond the limitations placed on where they could take their samples.

But one of the diplomats said the fact that the agency had requested fresh access to another part of the site suggested there are continued open questions about the nature of the work conducted at Parchin.

"The inspectors want to go back to another explosives bunker" that they apparently were not granted access to last week, the diplomat said on condition of anonymity.

In leaks to media last year, U.S. intelligence officials said a specially secured site at Parchin may be used in research for high-explosive components of nuclear weapons.

Iran asserts its military is not involved in nuclear activities, and the IAEA has found no firm evidence to the contrary. The agency also has not been able to support U.S. assertions that nearly two decades of covert nuclear programs discovered 2 ½ years ago were aimed at making nuclear weapons and not at generating electricity, as Tehran claims.

But an IAEA report in October expressed concern about published intelligence and media reports relating to equipment and materials that could serve military purposes.

At the time, diplomats said the phrasing alluded to Parchin.

As part of his investigation into Iran's nuclear activities, IAEA head Mohamed ElBaradei (search) has produced a series of reports for guidance by the IAEA board on what to do about Iran's nuclear activities.

His refusal to declare Iran in breach of the Nuclear Nonproliferation Treaty (search) has angered U.S. officials by derailing their drive to have the U.N. Security Council examine Iran's nuclear dossier.