The shock presidential election showing by Tehran's right-wing Mayor Mahmood Ahmadinejad was the result of an elaborate plot to rig the polls, defeated reformist contenders claimed Saturday.

"There has been bizarre interference. Money has changed hands," the centrist-reformist cleric and former parliament speaker Mehdi Karoubi told reporters in an unprecedented allegation.

"They can go and file a lawsuit against me, but I will give all the names of the people in power in my defence," he said defiantly.

His claim came as Ahmadinejad, an austere hardliner, bucked predictions and was placed second out of the seven candidates who stood in Friday's election. He will go into a run-off next Friday against moderate conservative cleric Akbar Hashemi Rafsanjani.