In a move that could alter the political landscape before elections in June, a powerful politician who once backed Mohammad Khatami for president has aligned himself with Khatami's rival in the reformist camp.
The shift comes despite the widely held belief that the charismatic Khatami would be a more formidable challenger to President Mahmoud Ahmadinejad, who has captured the support of the poor by distributing aid and is backed by conservative elements of society.
The reformist who switched candidates, Gholamhossein Karbaschi, was mayor of Tehran from 1988 to 1998 and was instrumental in Khatami's landslide presidential victory in 1997. Karbaschi said last week that this time he was supporting Mehdi Karroubi, a former speaker of Parliament.
"I think Karroubi would be a better candidate and more suitable for the country," Karbaschi said in a telephone interview.
The new alliance reveals the deep divisions among reformists who want more openness in Iranian politics and society.
The Associated Press reported Tuesday that another reformist, a former prime minister, Mir Hossein Mousavi, would also challenge Ahmadinejad. Mousavi was prime minister in the 1980s, during the Iran-Iraq War, and is seen by many as a strong candidate in the election because he was once a hard-liner and could siphon votes away from Ahmadinejad's base. He announced his intention to run in a statement made available to The Associated Press.
Some former supporters of Khatami, especially campaigners who were jailed during his presidency, said they would vote for Karroubi in the hope that he would be a more effective leader. They noted that during Khatami's two terms in office, from 1997 to 2005, his agenda was blocked by the conservative establishment and hamstrung by his perceived weakness.
Many of Khatami's allies, including Karbaschi, were jailed during the eight years that he was in office. Former supporters of Khatami say he failed to help them, while Karroubi, then the speaker of Parliament, backed them more strongly.
Emadedin Baghi, a human rights advocate and journalist who once supported Khatami, said, "Karroubi is a man who has helped more than anyone else with human rights cases and helped save people who were on the death row."
Karbaschi was tried in 1998 on corruption charges, sentenced to two years in prison and banned from holding public office for 10 years.