Iran announced Wednesday that its constitutional watchdog approved three prominent candidates to run against President Mahmoud Ahmadinejad in the upcoming June election, setting the stage for a showdown between reformists and hard-liners who have both criticized the current leader. Hard-liners have used the Guardian Council in the past to block reformist candidates who favor improving ties with the West and relaxing restrictions at home. But the group approved the two most prominent reformists candidates, Mir Hossein Mousavi and Mahdi Karroubi, likely because they were too high-profile to reject. The watchdog also approved a well-known conservative candidate, Mohsen Rezaei, a former leader of Iran's elite Revolutionary Guards who has joined his reformist competitors in criticizing Ahmadinejad for mismanaging Iran's economy. The group rejected 471 other candidates who wanted to run, including illiterate peasants, a 12-year-old boy and 42 women, the Interior Ministry said in a statement. Reformists, who believe they have a strong chance of defeating Ahmadinejad, have also criticized the president for spending an inordinate amount of time and energy slamming the West. They say his behavior has isolated Iran and believe he should have focused on battling rising unemployment and inflation in the country. Mousavi, a former prime minister who is seen as the leading challenger to Ahmadinejad, has said he would reshape Iran's policies and restore the country's dignity. His reformist counterpart, Karroubi, is a former parliamentary speaker who has said he would sit down with President Barack Obama if it served Iran's interests. The Obama administration has stepped up its efforts to engage Iran diplomatically, hoping to convince the country to suspend its nuclear program, which many in the West believe is focused on building weapons capability - a charge denied by Iran. Rezaei is not seen as having a good chance to win, but reformists hope he will weaken Ahmadinejad by siphoning votes from the incumbent's conservative base.