Tehran  - One week ahead of presidential elections, Iranian President Mahmoud Ahmadinejad and the opposition on Friday traded insults and accusations in an increasing acerbic campaign.

The opposition has accused Ahmadinejad of following an "immoral" election campaign.

The president was quick to hit back, claiming that his opponents have pursued a smear campaign against him during the last four years.

"There has been a circle ruling over the country, but I broke the chain ... four years ago," Ahmadinejad said in an election programme Friday on state television.

No names were mentioned, but it was clear that the president was referring to his predecessors - Mohammad Khatami and Akbar Hashemi- Rafsanjani - who are backing Ahmadinejad's main challenger Mir- Hossein Moussavi.

"This circle has availed itself of its financial power to pursue a (smear) campaign and did whatever possible to harm my government," Ahmadinejad said.

In a televised debate Wednesday, he accused Rafsanjani and his children of corruption, alleged that former reformist president Khatami pretended to be a doctor without actually having a doctorate, and claimed Moussavi's wife, Zahra Rahnavard, held a bogus doctorate.

"This is indeed an immoral approach in the pre-election time, which could even reach dangerous dimensions," Rahnavard said, displaying her doctorate issued by the Tehran Free University in 1995.

"I am really wondering whether the country has no other problems than my academic degree," she said.

The heated debate between Ahmadinejad and Moussavi has so far been the highlight of the election campaign in the runup to polls on June 12.

For the first time in Iran's post-revolution history, the president was harshly criticized by an opponent on live television. Moussavi said Ahmadinejad's performance was a source of humiliation for the Iranian people, for whom he "truly felt sorry."

The background of the "doctorate battle" involves former interior minister Ali Kordan, who was forced to resign last year after allegedly presenting a false doctorate to parliament. He claimed to have an honorary doctorate from Oxford University.

It was a huge embarrassment for Ahmadinejad's government and has been frequently used by the opposition during the campaign.

Supreme Leader Ayatollah Ali Khamenei, without explicitly mentioning Ahmadinejad, on Thursday called on the candidates to refrain from accusations and insults.

On Friday, Ahmadinejad labelled Rafsanjani a "power-grabber" and said he perpetuated "an aristocratic system." Rafsanjani had entered the 2005 presidential race as the favourite, but suffered a bitter defeat to Ahmadinejad, who was at the time Tehran's mayor and a political unknown.

Rafsanjani's brother, Mohammad Hashemi, told Mehr news agency that the family would sue the president after the elections. But Ahmadinejad was unimpressed by the warning. "These people should be sacrificed for the sake of national interests and not vice-versa - everybody should know about their eternal disgrace," he said.

He also rejected his opponents' claims about the widening economic crisis and high inflation. "The economic structure of the country should have been amended and this is what I did, and inflation is not more than 15 to 16 per cent," he said.

He said the current inflation rate was lower than that during the Khatami administration from 1997-2005. (dpa)