A powerful former president said Saturday he will sue hard-line leader Mahmoud Ahmadinejad for slander over remarks he made during an election debate.

In the latest obstacle to his campaign for re-election, Ahmadinejad has found himself in a bitter confrontation with Akbar Hashemi Rafsanjani and another former president, reformist Mohammad Khatami, neither of whom are candidates in Friday's vote.

In a highly charged televised debate on Wednesday, Ahmadinejad accused Rafsanjani, his sons and several other former top officials of corruption. It was an unusual move, given that Iranian politicians often avoid mentioning names in their attacks on opponents.

An outraged Rafsanjani rejected the accusations as "a complete set of lies" and demanded equal airtime to respond. On Saturday he went a step further, announcing that he and his sons will sue the president for slander.

Rafsanjani is a powerful figure in Iran's clerical leadership and is considered an influential political insider. He lost to Ahmadinejad in 2005 and has not publicly backed any candidate this time around, but he is believed to support anyone against Ahmadinejad.

He is the head of the State Expediency Council, a body that arbitrates between the parliament and an oversight body known as the Guardian Council. Rafsanjani, who held the presidency from 1989-97, also heads the Assembly of Experts, one of the cleric-run bodies that is empowered to choose or dismiss Iran's supreme leader.

In a statement released Saturday, Rafsanjani said Ahmadinejad has trampled on his presidential oath to protect the honor of all citizens.

"Given the explicit violation of the constitution and the trampling of the presidential oath ... definitely the charges will be pursued through legal and competent authorities," the statement said.

It did not say when the lawsuit would be filed, but Rafsanjani's brother, Mohammad, said the former president and his sons would do so after the election to avoid any accusations that they were out to sabotage Ahmadinejad's campaign.

A former conservative parliamentary speaker, Ali Akbar Nateq Nouri, says he is also planning to sue the president over similar accusations Ahmadinejad aired against him.

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. He is up against a strong challenge by reformists who seek better ties with the West and greater freedoms at home.

Seeking to distract voters from the ailing economy, Ahmadinejad has chosen to focus on his nation's advancements in nuclear technology, while slamming previous governments.

He has attacked his predecessor, Khatami, for a 2003 deal his government made with Europe to suspend Iran's uranium enrichment program. Ahmadinejad said Khatami played into "colonial policies" designed by enemies bent on "finishing" the Iranian nation.

Reformists countered that the deal was a temporary step that saved Iran from U.N. punishment, while allowing it to continue to develop other parts of its nuclear program. And they say Ahmadinejad, who restarted uranium enrichment after taking over as president, has brought the country more isolation and sanctions because of his hard-line policies and antagonism with the West.

The United States and some of its allies believe Iran aims to use enrichment technology to make bombs, though Iran denies that and says it is only pursuing peaceful nuclear energy.

During Wednesday's debate, the president's main reformist challenger, Mir Hossein Mousavi, accused him of driving Iran toward "dictatorship" and hurting its standing in the world by questioning the Holocaust.

In addition to Mousavi, a former prime minister in the 1980s, Ahmadinejad's other reformist rival is Mahdi Karroubi, a former parliamentary speaker. The sole conservative challenger is Mohsen Rezaei, a former Revolutionary Guards commander.