TEHRAN, Iran - A powerful former Iranian president urged the country's top leader Tuesday to take "serious action" against hard-line President Mahmoud Ahmadinejad for accusing current and former top government officials of corruption in a televised election debate.

Akbar Hashemi Rafsanjani, a powerful figure in Iran's clerical leadership, increased the political tension in an already highly charged campaign by going directly to the supreme leader, who has the final say in state matters and normally stays above the political fray.

In the rare, written appeal to Ayatollah Ali Khamenei, Rafsanjani said the president's corruption charges threatened to undermine the country's Islamic ruling system and could even target the supreme leader.

Rafsanjani, a moderate conservative, has long been a rival of Ahmadinejad, whom he lost to in the 2005 presidential election in a bitter run-off vote.

The letter comes as Ahmadinejad is fighting a tough battle for re-election in Friday's vote and is facing backlash from some for his political campaign mudslinging against his opponents and their allies.

In a televised debate with his top opponent, Mir Hossein Mousavi, on Wednesday, Ahmadinejad accused Rafsanjani, his sons and several other former top officials of corruption. The former president, who retains significant power in Iran, responded on Saturday by saying he and his family would sue Ahmadinejad for slander.

Ahmadinejad's bid for re-election has been burdened by Iran's stumbling economy and accusations from rivals that his confrontational policies have left Iran with few friends in the world.

"You are expected, given your position, responsibility and character, to take serious action to resolve this problem in a manner you deem appropriate and in order to confront dangerous seditions and extinguish a fire whose smoke is visible and stop this fire from flaring during and after the election," Rafsanjani said in the letter to Khamenei, a copy of which was made available to The Associated Press.

Rafsanjani called Ahmadineajd's remarks "a whole set of lies" and "irresponsible" and warned Khamenei that even his reputation was threatened by Ahmadinejad.

"Notable in these slanders is that the position of the supreme leader ... has been targeted," Rafsanjani said.

Reformists and many conservatives say Ahmadinejad's campaign tactics have tarnished the country's image and that his accusations against Rafsanjani and other current officials gives the impression that the whole Islamic ruling system is corrupt - including Khamenei.

"By accusing a long list of top officials of corruption, Ahmadinejad has effectively questioned the financial health of the whole ruling system including Khamenei," said political analyst Saeed Leilaz.

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