TEHRAN (Reuters) - Iran's reformist opposition leaders vowed to press on with legal challenges to an election they say was rigged, although the hardline government appeared on Thursday to have largely crushed mass street protests.

The unrest has exposed unprecedented rifts within Iran's clerical establishment, with Supreme Leader Ayatollah Ali Khamenei, who normally stays above the political fray, siding strongly with anti-Western President Mahmoud Ahmadinejad.