"President Mahmoud Ahmadinejad received praise from Iranian opposition politicians and withering criticism from its conservatives after he sent Barack Obama a letter last week congratulating him on winning the U.S. presidential race.

But in a sign that conservatives fear their attacks might inadvertently strengthen a possible opposition candidate in Iran's own presidential vote in June, their criticism has quickly shifted to early support for Ahmadinejad's re-election.

The potential opponent is former President Mohammad Khatami, the moderate whom Ahmadinejad bested in the last elections, in 2005. Khatami has not yet announced his candidacy, but is under pressure from his political allies to run.