VIENNA (Reuters) - A U.S. think tank said Iran might be cleaning up its Parchin military site, where some countries suspect experiments may have taken place in a possible atomic weapons programme, but Iran denied this on Thursday.
The U.S.-based Institute for Science and International Security (ISIS) pointed to satellite images showing vehicles and container-like objects being moved at Parchin. Iran said this was part of road works in the area.
The images were taken after Iran signed a major deal with world powers on July 14 to curb its nuclear activities in exchange for sanctions relief, ISIS said.
Such activity might complicate the work of the U.N.'s International Atomic Energy Agency (IAEA), which is tasked with judging whether Iran's past atomic activity had any military dimensions, including through access to Parchin.
"This renewed activity occurring after the signing of the (July 14 deal) raises obvious concerns that Iran is conducting further sanitisation efforts to defeat IAEA verification," the Washington-based think tank said in a report.
"This renewed activity may be a last ditch effort to try to ensure that no incriminating evidence will be found," said ISIS, which was founded by a former IAEA nuclear inspector to bring scientific expertise to debates about nuclear weapons.
Iran's mission to the United Nations in New York issued a statement saying it "strongly denies and rejects the baseless claims about the so-called clean-up operations in the Parchin Military Complex".
It said there was construction work at Parchin to repair a road and denounced "the extensive vicious campaign at work ... to poison the positive environment at the global level."
"The Islamic Republic of Iran.. has never had any military nuclear activity and has never been engaged in any unconventional act that would need a hasty cover-up," it added.
U.S. State Department spokesman Mark Toner, asked on Wednesday about Parchin, declined to comment on the issue.
White House deputy national security advisor Ben Rhodes told broadcaster CNN on Wednesday that Iran was not able "to clean up in a couple of weeks in Parchin something that they weren't able to try to clean up over the last decade."
According to data given to the IAEA by some member states, Parchin might have housed hydrodynamic experiments to assess how specific materials react under high pressure, such as in a nuclear blast.
A diplomat familiar with the Iran file said that the images showed the difficulty of implementing the July deal. "Old habits die hard," he said, referring to Iran, which in the past had failed to declare some of its nuclear activities to the IAEA.
The Vienna-based agency, which had no immediate comment on the ISIS report, said in its latest extensive Iran report that it continued to observe vehicles and construction material at Parchin and that activities there since 2012 are likely to have undermined its ability to conduct verification.
As a precondition to full sanctions relief, Tehran must provide sufficient information to the IAEA by Oct. 15 to allow it to prepare a final report on its past nuclear programme.
The Obama administration is defending the nuclear deal with Iran against strong opposition by some lawmakers who also criticise the IAEA for not releasing its own agreement with Iran to resolve concerns about Iran's nuclear past.
"I explained that my legal obligation is to protect safeguards confidentiality and this is an essential element of the international safeguards regime," IAEA head Yukiya Amano said after meeting U.S. politicians this week.