At least five of the Americans taken hostage in 1979 say they believe Mahmud Ahmadinejad was one of their captors.
One former hostage, retired U.S. Navy Captain Donald Sharer, told U.S. NBC television on 29 June that he remembers Ahmadinejad on two specific occasions.
"One of our guards let us pace the hallway outside of our jail cell up to another jail cell, where [fellow hostage] Tom Ahearn was, and we did that for a couple of days," Sharer said. "One day this fellow comes in while we are doing it and just chews out the guard very vehemently and he says in Farsi -- and Chuck, Colonel Scott [Chuck Scott, the embassy's military attache], interpreted for me -- he called us pigs and dogs and said we deserved to be locked up all the time. With something like that, a certain amount of fear seeps into your heart wondering what is going to happen next. Well, we got locked up and -- you tend not to forget people that kind of put your life in threat."
Another former hostage, Kevin Hermening, has said Ahmadinejad was involved in his interrogation the day he was taken captive.
But several former student leaders who were involved in the seizure of the U.S. Embassy say Ahmadinejad played no role.
Abbas Abdi, one of the best known of the former student leaders, is quoted by "The New York Times" as saying that Ahmadinejad wanted to take part in the U.S. Embassy takeover, but was rejected.
Abdi said Ahmadinejad "called after the embassy was captured and wanted to join us, but we refused to let him come to the embassy or become a member of our group."
Mohammad Ali Seyyednejad, one of the five founding members of the central council of Iran's largest student association, the Office to Foster Unity, has a different account of the events.
He told Radio Farda that Ahmadinejad was against the embassy takeover.
"Mr. Ahmadinejad was a member of the initial founding council of Office To Foster Unity, and later, when the issue of the occupation of the U.S. Embassy was put on the agenda of a central council meeting, Mr. Ahmadinejad and I were among the opponents of the embassy occupation," Seyyednejad told Radio Farda.
The U.S. Embassy in Tehran was stormed on 4 November 1979 by a group of student activists calling themselves the Student Followers of the Imam [Khomeini]'s Line.
They took the staff hostage, accusing them of engaging in espionage. The students said they were protesting against U.S. interference in Iran's internal affairs.
Questions about Ahmadinejad's role in the U.S. Embassy occupation were raised in recent days after a photograph of a bearded hostage-taker leading a blindfolded American hostage was published on several websites.
Some believe the hostage-taker is Ahmadinejad, but others, including some of his aides, have dismissed the claim. Photos of Ahmadinejad from that time published on his website (http://www.mardomyar.com) show little resemblance.
On 30 June, U.S. President Bush said the accusation against Ahmadinejad "raises many questions." The U.S. State Department then called on the Iranian government to clarify the role of Ahmadinejad in the 1979 siege.
The allegations against Ahmadinejad are unlikely to cause public outrage in Iran.
Several participants in the embassy siege are now prominent politicians, including Massoumeh Ebtekar, a vice president and head of Iran's environmental protection organization.
Some went on to become reformists, including Abbas Abdi, who was recently released from jail after serving time for organizing a poll showing that most respondents favored restoring ties between Iran and the United States.
For Americans, the 1979 hostage taking sparked a political crisis that led to the rupture of diplomatic ties between Washington and Tehran.
U.S. State Department spokesman Sean McCormack said on 30 June the American government is working to establish the truth about Ahmadinejad's alleged involvement in the hostage crisis.
He added that the government had "not forgotten" that so many of its diplomats were taken hostage and held for "more than a year."
Sonia Sceats is an associate fellow at the international law program at Chatam House, the Royal Institute of International Affairs, in London. She told RFE/RL the accusations against Ahmadinejad could further damage already strained relations between Iran and the United States.
"If there is strong enough evidence [linking Ahmadinejad to the hostage-taking] it will place limitations on his travel, because if he travels to a country which, for example, recognizes international jurisdiction over a crime of that nature, he may face being arrested, charged, and tried in that country," Sceats said. "Or he may face extradition to the United States, where certainly the federal courts recognize international jurisdiction over the crime of hostage-taking."
Iranian officials have yet to react to the allegations against Ahmadinejad.
(Radio Farda correspondent Mossadegh Katouzian contributed to this report.)
For RFE/RL's full coverage of Iran's elections, see "Iran Votes 2005"