Iran has granted U.N. nuclear inspectors new access to a high-security military site as part of efforts to avoid referral to the Security Council, diplomats said Wednesday.

The diplomats said experts of the International Atomic Energy Agency were allowed to revisit Parchin as they try to establish whether Tehran has a secret nuclear weapons program.

Parchin has been linked by the United States and other nations to alleged experiments linked to nuclear arms. The IAEA had for months been trying to follow up on a visit in January for further checks of buildings and areas within the sprawling military complex as it looks for traces of radioactivity.

That visit -- which was closely controlled by authorities -- revealed no such traces.

But one of the diplomats -- who like the others requested anonymity because he was not authorized to talk to the media about the sensitive investigation -- said that over the past few days IAEA inspectors "gained access to buildings" previously out of bounds to them.

The diplomat, who is close to the agency, said environmental swipes were taken from objects in the buildings and would be analyzed at IAEA laboratories.

If those swipes reveal minute amounts of radioactivity, they would strengthen suspicions of nuclear-related work at Parchin.

Because Parchin is run by the country's armed forces, such a discovery would weaken Iranian arguments that its nuclear programs are strictly nonmilitary. That, in turn, would strengthen sentiment that Tehran be referred to the U.N. Security Council for breaching the Nuclear Nonproliferation Treaty as early as Nov. 24, when the IAEA's 35-nation board of governors has scheduled its next meeting. The swipe results are expected before then.

U.S. intelligence officials said last year that a specially secured site on the Parchin complex, about 30 kilometers (20 miles) southeast of Tehran, may be used in research on nuclear arms, specifically in making high-explosive components for use in such weapons.

The IAEA has not found any firm evidence to challenge Iranian assertions that its military is not involved nuclear activities, but in a document last year has expressed concern about reports "relating to dual use equipment and materials which have applications ... in the nuclear military area." Diplomats said that phrasing alluded to Parchin.

Before the next board meeting, IAEA inspectors also hope to be allowed to visit Lavizan-Shian, suspected of being the repository of equipment bought by its military that could be used in a nuclear weapons program

The State Department last year said Lavizan-Shian's buildings had been dismantled and topsoil had been removed from the site in attempts to hide nuclear-weapons related experiments. Agency officials subsequently confirmed that the site had been razed, but Iran said work at the site, on the outskirts of Tehran, was part of construction unrelated to military or nuclear matters.

Iran is under increasing pressure before the next IAEA board meeting to show it is cooperating with a more than three-year IAEA probe of nearly 18 years of suspected clandestine nuclear activities as it tries to derail a U.S.-backed European push to report it to the Security Council.

Russia and China -- council members who also sit on the IAEA board -- are opposed to such a move. But calls last week by Iranian President Mahmoud Ahmadinejad called for Israel to be "wiped off the map," have strengthened the U.S.-European hand by focusing on concerns over Iran's nuclear ambitions. Russia was among the dozens of nations protesting his statements.