Mystery surrounds an Iranian scientist, Shahram Amiri, who went missing in 2009, amid protests from Tehran that he had been kidnapped by US agents. Other reports suggested he had defected to the US.
Here is a chronology of events.
Iran's Foreign Ministry says Mr Amiri has left the US and will arrive back in Iran via a third country.
Mr Amiri turns up in the Iranian interests section of the Pakistani embassy in Washington and demands to go back to Iran.
Iranian state radio reports that Mr Amiri has said in a telephone interview from inside the Iranian interest section that he has been "under enormous psychological pressure and supervision of armed agents in the past 14 months".
In the US government's first public acknowledgement that Mr Amiri is in the US, Secretary of State Hillary Clinton says: "Mr Amiri has been in the United States of his own free will and he is free to go."
A man claiming to be Mr Amiri resurfaces on another video shown on Iranian state television, this time claiming he has escaped from US custody in the US state of Virginia and is in hiding.
"Presently, I am producing this video in a safe place," he says.
"I could be re-arrested at any time."
A man claiming to be Mr Amiri appears in a video posted online, claiming he was kidnapped by CIA agents during the Hajj.
"They took me to a house located somewhere that I didn't know," he says in the video. "They gave me an anaesthetic injection."
He says he is living in Tucson, Arizona, and says he has been subjected to eight months of "the most severe tortures and psychological pressures".
But another video message appears on YouTube on the same day, recorded apparently by the same man, entirely contradicting this version of events.
In this video, he says he is in the US to continue his education, adding: "I am free here and I assure everyone that I am safe."
He says he is "not involved in weapons research and have no experience and knowledge in this field".
US television network ABC reports that Mr Amiri has defected to the CIA and has settled in the US, citing anonymous officials briefed by intelligence agents.
ABC says the scientist has been extensively debriefed and has helped to confirm US intelligence assessments about the Iranian nuclear programme.
At a news conference, Mr Mottaki accuses the US of abducting Mr Amiri, citing "existing pieces of evidence that we have at our disposal".
"We expect the American government to return him," he says.
Mr Mottaki and the speaker of Iran's parliament, Ali Larijani, accuse Saudi Arabia of complicity in the alleged abduction, saying he was taken from Saudi soil.
The Saudis deny the accusation and the US government declines to comment on the issue.
"We are aware of the Iranian claims," US state department spokesman Philip Crowley says. "I have no information on that."
Iranian Foreign Minister Manouchehr Mottaki publicly suggests for the first time that Mr Amiri is being held by the US authorities.
Meanwhile, the Saudi-owned al-Sharq al-Awsat newspaper reports that Mr Amiri has sought asylum in Saudi Arabia.
The Iranian government announces Mr Amiri has disappeared. Referring to the scientist only as an "Iranian citizen", Iran's semi-official Fars news agency suggests he is being held in Riyadh, the Saudi capital, and says it holds the Saudi authorities "accountable" for his disappearance.
The agency quotes Mr Amiri's wife as complaining that Saudi Arabia was unable to safeguard pilgrims' security during visits to holy sites in the country.
The scientist, in his early 30s, disappears while undertaking the Hajj pilgrimage in the Saudi Arabian city of Mecca, soon after telephoning his wife in Iran.