TEHRAN, Iran -- Iranian President Mahmoud Ahmadinejad lashed out at President Barack Obama yesterday, warning him against "interfering" in Iranian affairs and demanding an apology for criticism of a government crackdown on demonstrators protesting alleged electoral fraud.

Despite an increasingly harsh response to the protests, opposition leader Mir Hossein Mousavi pledged to continue challenging official results that showed a landslide victory for Mr. Ahmadinejad in Iran's June 12 presidential election. He vowed to resist growing pressure to end his campaign and said he remains determined to prove that those who rigged the election are also responsible for the violence unleashed on opposition protesters.

The two rivals issued their dueling statements -- neither mentioning the other by name -- a day after security forces broke up the latest demonstrations, then temporarily detained university professors who had met with Mr. Mousavi.

Two grand ayatollahs, leading figures in Iran's predominant Shiite Muslim faith, also waded into the fray yesterday, as did European foreign ministers from the Group of Eight world powers at a meeting in Italy.

In a speech at a petrochemical plant in southern Iran, Mr. Ahmadinejad said Mr. Obama was behaving like his predecessor, former President George W. Bush, and suggested that talks with the United States on Iran's nuclear program would be pointless if the U.S. president kept up his criticism.

Mr. Obama, who has expressed interest in talking to the Iranian leadership about the nuclear issue, told a news conference Tuesday that he was "appalled and outraged" by recent violence against demonstrators, and he accused the Iranian government of trying to "distract people" by blaming the unrest on the United States and other Western nations.

"Do you want to speak with this tone?" Mr. Ahmadinejad responded yesterday, addressing Mr. Obama. "If that is your stance, then what is left to talk about?" He added, "I hope you avoid interfering in Iran's affairs and express your regret in a way that the Iranian nation is informed of it."

He asked why Mr. Obama "has fallen into this trap and repeated the comments that Bush used to make" and told the U.S. president that such an attitude "will only make you another Bush in the eyes of the people."

Mr. Ahmadinejad also praised Iran's election as demonstrating "the great capabilities and grandeur of the Iranian nation" and declared that his country is practicing true "freedom," as opposed to "this unpopular democracy which is governing America and Europe." Americans and Europeans "have no right to choose and are restricted to ... two or three parties" in voting for their leaders, he said.

In Washington, White House spokesman Robert Gibbs dismissed Mr. Ahmadinejad's criticism. Mr. Obama has said "that there are people in Iran who want to make this not about a debate among Iranians in Iran, but about the West and the United States," Mr. Gibbs said. "And I would add President Ahmadinejad to that list of people trying to make this about the United States."

Iran's government has declared that Mr. Ahmadinejad decisively won the June 12 election with nearly 63 percent of the vote, while Mr. Mousavi received less than 34 percent, and two other candidates trailed far behind. Mr. Mousavi immediately challenged those results, charging that massive fraud "reversed" the outcome and cheated him of victory.

The 67-year-old former prime minister posted a statement on his Web site yesterday saying he was being pressed to withdraw his challenge and had been severely restricted in his ability to communicate with supporters. "However, I am not prepared to give up under the pressure of threats or personal interest," he said.

"The truth ... is that a major fraud has taken place in these elections, and the people who tried to show their dismay with this event were attacked, killed and arrested," Mr. Mousavi said. "Not only am I not scared of responding to their false accusations, but I'm ready to show how the people responsible for the presidential fraud" are also to blame for having "spilled the blood of the people." Mr. Mousavi asked his followers to "continue your legal and responsible protest, which is born out of the Islamic revolution, with calm and by avoiding trouble."

His Web site also said 70 academics were arrested Wednesday night and early yesterday after meeting with him. It said authorities subsequently released all but four, and that those still detained included Mr. Mousavi's former campaign manager.

The pro-government Fars News Agency denied the account. Quoting an "informed source," it said prosecutors questioned "certain participants" after Mr. Mousavi's meeting with members of the Islamic Association of University Lecturers, but that "none of the said people were arrested."

A senior Shiite cleric, Grand Ayatollah Nasser Makarem-Shirazi, called for the election dispute to be settled through "national reconciliation," saying in a statement yesterday that recent events "have caused deep regret and sorrow in all Iranians loyal to the Islamic establishment and revolution ... and have gladdened the enemy," state-run Press TV reported. "Definitively, something must be done to ensure that there are no embers burning under the ashes" and to turn "hostilities, antagonism and rivalries ... into amity and cooperation," he said.

But a leading dissident cleric, Grand Ayatollah Hossein Ali Montazeri, said an "impartial" committee should resolve the election dispute, which he warned could ultimately undermine the government if it is not addressed. "If Iranians cannot talk about their legitimate rights at peaceful gatherings and are instead suppressed, complexities will build up which could possibly uproot the foundations of the government, no matter how powerful," Agence France-Presse quoted Ayatollah Montazeri as saying.

At a G-8 meeting in Trieste, Italy, foreign ministers sought to forge a united stand against the Iranian crackdown but ran into opposition from Russia. Italian Foreign Minister Franco Frattini said Iran "must now choose whether or not it wants to keep the door open to dialogue with the international community, because the open hand from the United States, that we supported, must not be greeted with a hand covered in blood."

British Foreign Secretary David Miliband deplored a "profound clampdown" in Iran and said a "crisis of credibility" is dividing Iran's government from its people.

But Russian Foreign Minister Sergey Lavrov opposed any condemnation of Tehran, saying after talks with Mr. Frattini that "isolating Iran is the wrong approach."

The streets of Tehran were largely quiet yesterday after another opposition presidential candidate, Mehdi Karroubi, postponed plans for a demonstration to mourn protesters killed by security forces. Mr. Karroubi said he has not "succeeded in booking a particular location" for a mourning ceremony, apparently because the government has banned demonstrations. He said he still wants to organize a gathering that would "match the dignity of the martyrs of the past few days," and he said a date and time would be announced later.

Mr. Karroubi also charged that the government has acted illegally in banning demonstrations and arresting political activists. He called for the immediate release of political detainees, and he challenged the Interior Ministry to allow separate but simultaneous demonstrations by Ahmadinejad supporters and the opposition to see which side would draw more people.

At least 17 people have been reported killed in violence following the June 12 elections, state-run media have reported. But Press TV, an English-language version of state television, put the death toll at 20 and quoted "informed sources" as saying eight of the dead were members of the pro-government Basij militia. There was no independent confirmation of the claim, which marked the first mention in official media of deaths among security forces in the recent violence.