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Satellite surveillance has shown an increase in activity at an Iranian site suspected of links to alleged secret work on nuclear weapons, officials tell The Associated Press.

One of the officials cited intelligence from his home country, saying it appeared Tehran is trying to cover its tracks by sanitizing the site and removing any evidence of nuclear research and development. Counterparts from two other countries confirmed sightings of increased activity but said they did not have reasons to believe it was linked to such efforts.

Their focus is on a structure believed to be housing a large metal chamber at a military site that a Nov. 8 International Atomic Energy Agency report described as being used for nuclear-related explosives testing.

Officials from the three IAEA member countries say that recent satellite imagery of the site, at Parchin, southwest of Tehran, shows increased activity, including an unusual number of vehicles arriving and leaving. One of the officials described the movements, recorded Nov.4-5, as unusual and said his country views it as evidence that Iran is trying to "clean" the area of traces of weapons-related work

"Freight trucks, special haulage vehicles and cranes were seen entering and leaving... (and) some equipment and dangerous materials were removed from the site," said a summary he provided to the AP.

His counterparts agreed there had been more activity than usual at the site around that date but could not conclude that pointed to an attempted cover-up by the Iranians.

The IAEA was alerted to the suspicions late last week and a senior diplomat familiar with the issue said the agency was closely monitoring all suspect sites mentioned in the agency's report. He, like the officials, asked for anonymity because his information was confidential.

The IAEA said it would have no comment. Ali Asghar Soltanieh, Iran's chief delegate to the IAEA, dismissed the reports as "childish stories." He told the AP he had not heard of any such activity, describing the claims as "ridiculous."

The large complex is used for research, development, and production of ammunition, missiles, and high explosives. IAEA experts had already visited the Parchin site twice in 2005 and were allowed to pick several buildings at random for inspections that revealed nothing suspicious. But a former inspector who was part of that inspection told the AP that the site was too vast to be able to draw conclusions on the basis of such restricted and haphazard visits.

Iran -- which is under U.N. Security Council sanctions for refusing to stop work that could be used to arm nuclear warheads -- asserts it is interested only in producing energy. But it has refused for over three years to allow the IAEA to probe growing suspicions that it is conducting research and development of such weapons.

Summarizing such fears in a Nov. 8 report that first mentioned the steel chamber believed to be used for nuclear testing, the agency concluded that some of the alleged activities it listed could have no other purpose than to make the bomb.

Ahead of that report, on Oct. 30. Iran invited top IAEA investigator Herman Nackaerts to Tehran for talks "aiming at a resolution of matters." That would have given Nackaerts a chance to ask for a renewed trip to Parchin that included a visit to the suspected building.

On Friday, however, Soltanieh abruptly announced that the trip was postponed, if not canceled. He blamed the IAEA, saying it had "messed up" the trip by publishing its report.

The decision could give Iran time to clean up sites mentioned in the report as being part of the secret work, should it chose to do so. The senior diplomat said the IAEA was aware of that possibility -- even if the official reason for postponement given the agency by the Iranians was that domestic sentiment was too negative in the wake of the report for such a visit.

Such cleanups would not be new. Iran razed the Lavizan Shian complex in northern Iran, before allowing IAEA inspectors to visit the suspected repository of military procured equipment that could be used in a nuclear weapons program five years ago. Tehran said the site had been demolished to make way for a park, but inspectors subsequently found traces of uranium enriched to or near the level used in making the core of nuclear warheads.

The Iranians also embarked on an extensive redo at the Kalay-e Electric Co., just west of Tehran, before agency inspectors were given access nine years ago. Although the site was repainted and otherwise sanitized, samples taken from Kalay-e also showed traces of enriched uranium, though at levels substantially below warhead grade.

Based on the IAEA report, the agency's board on Friday expressed "deep and increasing concern about the unresolved issues regarding the Iranian nuclear program, including those which need to be clarified to exclude the existence of possible military dimensions." The concerns were voiced in a resolution supported by 32 of the 35 board nations.