By Dominic Evans and Fredrik Dahl
The comments were a further escalation in a war of words after Ahmadinejad, facing a strong challenge from former Prime Minister Mirhossein Mousavi, accused his rivals of using Hitler-style smear tactics and said they could face jail.
The campaign has shown up divisions among leading figures in the Islamic Republic, between backers of the hardline incumbent and more moderate advocates of detente with the West, whose supporters have spilled on to the streets for boisterous rallies.
"The presence of supporters of Mirhossein Mousavi on the streets are part of the velvet revolution," said Yadollah Javani, head of the Guards' political office, using a term used to describe the 1989 non-violent revolution in Czechoslovakia.
"Any kind of velvet revolution will not be successful in Iran," he said in comments published on the Guards' website.
Mousavi's supporters, dressed in his green campaign color, have taken to the streets of Tehran for nightly rallies, waving flags and banners and shouting anti-Ahmadinejad slogans.
There have been sporadic clashes in the capital but the campaign for Friday's election has been largely peaceful.
Describing the moderates and reformists as "extremists," Javani said they were "trying by launching a psychological media war to announce themselves as winner of this election."
Iran often accuses Western powers of seeking to undermine the Islamic state through a "soft" or "velvet revolution" with the help of intellectuals and others inside the country.
State television said that, as always at election time, all campaigning would be banned from Thursday morning. Cars plastered with pictures and campaign material would be stopped and seized, he said.
"HITLER'S METHODS"
Mousavi and two other candidates running against Ahmadinejad say he has lied about the state of the economy which is suffering from high inflation and a fall in oil revenues from last year's records.
In a speech in Tehran on Wednesday, Ahmadinejad said his rivals had broken laws against insulting the president and they could face jail. Insulting senior officials is a crime in Iran punishable by a maximum two-year jail sentence.
"Such insults and accusations against the government are a return to Hitler's methods, to repeat lies and accusations … until everyone believes those lies," the semi-official Fars news agency quoted him as saying.
Ahmadinejad has accused Mousavi's supporters, including former President Akbar Hashemi Rafsanjani, of corruption. Rafsanjani responded angrily, calling on the Islamic Republic's supreme leader Ayatollah Ali Khamenei to rein in Ahmadinejad.
Mousavi says Ahmadinejad has isolated Iran with his vitriolic attacks on the United States, his combative line on Iran's nuclear policy and his questioning of the Holocaust.
He advocates easing nuclear tension, while rejecting demands that Tehran halt nuclear work which the West fears could be used to make bombs. Iran, the world's fifth-largest oil exporter, says its nuclear programme is peaceful.
Friday's election will not change Tehran's nuclear policy, which is decided by Khamenei, but a victory for Mousavi could herald a less confrontational relationship with the West.
Mousavi, who had been out of the political spotlight since serving as prime minister during the 1980-88 war with Iraq, has attracted strong support and his sympathizers increasingly believe he could win the election.
The outcome remains unpredictable. The relatively unknown Ahmadinejad surprised everyone with his victory four years ago, and he has enjoyed Khamenei's support throughout his presidency.
Analysts say no candidate is likely to gain the 50 percent needed for an outright first-round victory, forcing a run-off between the two front-runners a week later.
They say that, even if Mousavi were to defeat Ahmadinejad, there would be no sudden change in relations with the West.
"Things in Iran move slowly. It would mark a significant change, but it wouldn't reflect regime change," said Ali Ansari of the University of St Andrews in Scotland.
(Editing by Charles Dick)
