VIENNA (Reuters) - A U.S. think-tank has published satellite images which it says underscore suspicions that Iran is trying to destroy evidence of possible nuclear weapons-related research at a site that U.N. inspectors have not been allowed to visit.
The Institute for Science and International Security (ISIS) posted the pictures on its website hours after the U.N. nuclear watchdog showed diplomats similar images that western envoys said indicated a clean-up at the Parchin military facility.
Parchin, which Iran says is a conventional military complex, southeast of Tehran, is at the centre of western allegations that Iran has conducted experiments - possibly a decade ago - that could help develop atom bombs. Iran denies any such ambition.
The new satellite images appear to back western suspicions that Iran is cleaning the site of any incriminating evidence, such as traces of uranium or other materials, before possibly allowing the International Atomic Energy Agency (IAEA) to go there.
Western diplomats who attended Wednesday's closed-door briefing by the IAEA in Vienna told Reuters that two small buildings at Parchin had been removed, and ISIS said its pictures from May 25, published on isis-online.org, showed that they "have been completely razed".
"Iran is worried that the agency might find something there. Otherwise it wouldn't be going through the sanitization process," a senior western official said.
The pictures have been published after inconclusive talks last week between Tehran and six world powers that aim to end a nuclear standoff in which the West has intensified sanctions on Iran, and Israel and the United States have threatened military strikes to stop the Islamic Republic getting the bomb.
The IAEA has repeatedly asked Iran for access to Parchin. Last week, a senior Iranian official was quoted as saying the IAEA had not yet given good enough reasons to visit the site.
Iran says its nuclear activities are for electricity production and medical applications and has so far refused to let inspectors visit Parchin, saying there must first be a broader agreement setting out how the IAEA's probe will progress.
IAEA Director General Yukiya Amano said after visiting Tehran last week that he expected soon to secure a framework deal to unblock the agency's investigation.
But the western official said Iran had not engaged with the U.N. agency to finalize the deal since Amano's visit.
"I'm not optimistic that Iran is going to provide that cooperation," the official said.
Iran's IAEA envoy, Ali Asghar Soltanieh, dismissed western suspicions of clean-up efforts at Parchin, telling reporters after the May 30 briefing at IAEA headquarters that "this kind of noise and allegations are baseless".
ISIS, which publishes research about nuclear proliferation, said the satellite images showed tracks "made by heavy machinery used in the demolition process."
The two buildings which now appear to have been dismantled - near the main structure that is of interest to the IAEA - were intact as recently as early April, it said.
"Heavy machinery tracks and extensive evidence of earth displacement is also visible throughout the interior as well as the exterior of the site's perimeter," ISIS said.
"The newest image raises concerns that Iran is attempting to raze the site prior to allowing an IAEA visit," it said.
Last week, the IAEA said in a report that satellite images showed "extensive activities" at the facility that could hamper its investigation.
Western diplomats said this was an allusion to suspected "sanitization" at Parchin that only started after the IAEA made its request for access to the site.
Another Iranian site, Lavizan-Shian, was completely razed in late 2003 and early 2004. Western diplomats said at the time that they suspected Iran was conducting undeclared nuclear activities at Lavizan and was determined to cover them up.
Iran has dismissed charges aired about Parchin as "childish" and "ridiculous".
An IAEA report last November said Iran had built a large containment vessel in 2000 at Parchin in which to conduct tests that the U.N. agency said were "strong indicators of possible (nuclear) weapon development."
It said a building was constructed around a large cylindrical object, a vessel designed to contain the detonation of up to 70 kg (150 lb) of high explosives. Diplomatic sources say the suspected tests likely took place about a decade ago.