VIENNA (Reuters) - The U.N. nuclear watchdog showed a series of satellite images on Wednesday that added to suspicions of clean-up activity at an Iranian military site it wants to inspect, Western diplomats said, but Tehran's envoy dismissed the presentation.
The pictures, displayed during a closed-door briefing for member states of the International Atomic Energy Agency (IAEA), indicated determined efforts in recent months to remove any incriminating evidence at the Parchin site, the diplomats said.
In the latest picture, from mid-August, a building where the IAEA believes Iran carried out explosives tests - possibly a decade ago - relevant for nuclear weapons development had been shrouded in what appeared to be pink tarpaulin, they said.
"It was pretty compelling," a senior Western diplomat said about the briefing by IAEA Deputy Director General Herman Nackaerts and Assistant Director General Rafael Grossi.
"The last image was very clear. You could see the pink," the envoy said.
The purpose of covering the building could be to conceal further clean-up work from overhead satellites, according to a U.S. think-tank, the Institute for Science and International Security (ISIS).
The IAEA said in a confidential report last week that "extensive activities" undertaken at Parchin since February - including the demolition of some buildings and removal of earth - would significantly hamper its investigation there, if and when it was allowed access to the facility southeast of Tehran.
Iran, which denies Western accusations that it seeking to develop the capability to make nuclear bombs, says Parchin is a conventional military site.
Iran's envoy to the IAEA, Ali Asghar Soltanieh, suggested the activities "claimed to be made in the vicinity of these so-called locations which are identified" by the IAEA had nothing to do with the U.N. agency's investigation.
"Merely having a photo from up there, a satellite imagery ... this is not the way the agency should do its professional job," he told reporters after the IAEA's briefing.
"Everybody should be careful not to damage (the) credibility of the agency," Soltanieh added.
Iran says it must first reach a broader agreement with the IAEA on how the Vienna-based U.N. agency should conduct its investigation into alleged nuclear bomb research in the Islamic state before it can possibly be allowed access to Parchin.
Last week's IAEA report said "no concrete results" had been reached in a series of high-level meetings with Iran over the past eight months on such a framework accord.
Highlighting one of the main sticking points, Soltanieh said Iran must see the documents which form the basis for the IAEA's concerns of possible military dimensions to the Islamic Republic's nuclear programme.
Diplomats say the IAEA is not able to hand over some of those files - which it is believed to have received from foreign intelligence services - because of confidentiality reasons.
"They have to deliver the documents," Soltanieh said, making clear that Iran could not otherwise agree to a deal. "Without documents we cannot prove whether this is baseless or not baseless. We should have the documents."
The IAEA report also said Iran had doubled the number of centrifuges at an underground uranium enrichment facility in the last few months, in defiance of international demands that it suspends the work.
Refined uranium can be used to fuel nuclear power plants, which is Iran's stated aim, or provide the explosive core for a nuclear warhead if processed further, which the West and Israel suspect is Tehran's ultimate aim.
(Editing by Jon Hemming)
This story has been refiled to fix typos in the sixth and 11th paragraphs