Shahram Amiri disappeared in Saudi Arabia in May during a pilgrimage to Mecca, prompting speculation he had defected to the West. His family have not heard from him since.
Iran's Foreign Minister, Manouchehr Mottaki, said yesterday Tehran had proof of Washington's involvement in Dr Amiri's disappearance.
"We have found documents that prove US interference with the Iranian pilgrim Shahram Amiri in Saudi Arabia," Mr Mottaki said.
"We hold Saudi Arabia responsible and consider the US to be involved in his arrest."
Dr Amiri is the second person involved in Iran's nuclear program to have disappeared while abroad in the past two years. The first was Ali Reza Asghari, a deputy defence minister and leader of the Revolutionary Guards, who vanished in Turkey two years ago.
Saudi Arabia and Turkey are two of the US's strongest allies in the region and the most outspoken on a possible Iranian military nuclear program.
Mr Mottaki lodged a complaint with the UN Secretary-General last month about four missing Iranians he claimed were being held in US custody. Dr Amiri and Mr Asghari were among them.
Speculation surrounding Dr Amiri's disappearance has heightened since Iran's public disclosure last month of a previously secret uranium enrichment plant near the holy city of Qom, with questions being asked about the nature of his nuclear work.
Dr Amiri worked as a nuclear physics researcher at Malek-e-Ashtar University, a research institute associated with the Iranian military. His family have said he researched the medical uses of nuclear technology, a project that links him to the research reactor for which Tehran is seeking a foreign supply of enriched uranium.
The Iranian Student News Agency yesterday reported rumours that Dr Amiri worked for Iran's Atomic Energy Organisation, while Jahan News, a conservative Iranian news website, reported Saudi officials as claiming he had sought political asylum there.
Others have pointed to the timing of the disappearance and subsequent revelations about Qom. When US President Barack Obama announced the discovery of the Qom site last month, he referred to the emergence of fresh information in the first half of the year.
"Earlier this year, we developed information that gave us confidence the facility was a uranium enrichment plant," Mr Obama said. The Iranians had declared the plant to the International Atomic Energy Agency days before, he said, after realising its cover had been blown.
US and British officials have attributed their knowledge of the Qom plant to technical data, satellite surveillance and intelligence operations.
Source: The Australian