VIENNA - A US security institute says commercial satellite imagery shows new activity at an Iranian military site which raises concern that the Islamic state may be "washing" a building the United Nations' nuclear agency wants to inspect.
The United Nations' International Atomic Energy Agency (IAEA) suspects nuclear weapons-related research may have taken place at the Parchin military complex southeast of Tehran.
Iran has dismissed the allegations but has yet to allow the agency to visit the facility, despite repeated requests.
IAEA chief Yukiya Amano said last week that the agency had recently noticed some "activities" there. He gave no details but Western diplomats suspect Iran may be cleaning the site before any inspection. Tehran denies this.
The Institute for Science and International Security (ISIS), a Washington-based think-tank specializing on nuclear proliferation, said it had acquired commercial satellite imagery from April 9 which back up the IAEA's concern.
"The new activity seen in the satellite image occurred outside a building suspected to contain an explosive chamber used to carry out nuclear weapons related experiments," it said on its website in a May 8 report including the satellite image.
Iran's mission to the IAEA was not immediately available for comment. It has previously dismissed allegations aired about Parchin as "childish" and "ridiculous".
The images showed items lined up outside a building and what appeared to be a stream of water, ISIS said.
"The items visible outside the building could be associated with the removal of equipment from the building or with cleansing it," it said.US sees Iranian obstruction
"The stream of water that appears to emanate from the building raises concerns that Iran may have been washing inside the building, or perhaps washing the items outside the building," ISIS said.
Previous satellite images from recent months did not show any similar activity at the building, indicating it is not a regular occurrence, it added.
The IAEA has said that gaining access to Parchin is a priority when it holds a new round of talks with Iran in Vienna next week after two previous meetings in Tehran failed to make any notable progress.
Western powers suspect Iran is seeking to develop the capability to make nuclear bombs. Iran, one of the world's largest oil producers, says its program is peaceful.
An IAEA report late last year revealed a trove of intelligence pointing to research activities in Iran of use in developing the means and technologies needed to assemble nuclear weapons, should it decide to do so.
One finding in the report was information that Iran had built a large containment chamber at Parchin in which to conduct high-explosives tests that the IAEA said are "strong indicators of possible weapon development".
A senior US official said on Tuesday that Iran must cooperate with the IAEA's investigation and provide access to relevant sites, personnel and documents.
"Iran continues to delay and obstruct that process," Thomas Countryman, assistant secretary for international security and nonproliferation, told a meeting in Vienna.