Ferociously policed street protests were replaced by razor-sharp rhetoric in Tehran today as President Mahmoud Ahmadinejad and his challenger, Mir Hossein Mousavi, launched fresh attacks on each other.

Mr Ahmadinejad, whose disputed election victory has prompted the biggest crisis in the 30-year history of the Islamic Republic, rounded on President Obama, after the US leader said he was "appalled and outraged" at the violence with which demonstrations have been repressed.

Then Mr Mousavi — who many claim is the rightful winner of the election but who has not been seen in public for a week — issued a statement protesting at the crackdown, the latest stage of which saw 70 university professors arrested last night as they left his home.

"I insist on the nation’s constitutional right to protest against the election result and its aftermath," said Mr Mousavi, a former Prime Minister under Ayatollah Khomeini who has become a figurehead for the protests despite his far-from-radical views. He also criticised the crackdown on the press, adding: "I strongly criticise the closure of the Kalame-ye Sabz daily newspaper and the arrest of those who worked there ... The illegal confrontation with the media opens the way for foreign interference."

Mr Mousavi also complained of "complete" restrictions on his access to people.

The latest arrests suggest that the suppression of dissent in Iran is not slackening off as street protests over the election dwindle, but is if anything intensifying. The academics arrested outside Mr Mousavi's house join more than 100 reformist journalists, academics and politicians already being held incommunicado in Tehran's Evin prison. They were rounded up at their homes and offices, some within hours of polling ending on June 12. Yesterday evening there were violent scenes in Baherestan Square, when a few hundred protesters were repulsed with gunfire, teargas and beatings by thousands of riot police and the hardline Basij volunteer militia who have played a key role in repressing unrest.

There has been condemnation in the West of the treatment handed out to protesters, and on Tuesday Mr Obama made his strongest comments yet, saying he was appalled by the scenes. Today Mr Ahmadinejad struck back and accused the US President of following his predecessor's lead.

"Mr Obama made a mistake to say those things. Our question is why he fell into this trap, and said things that previously (former President) Bush used to say," Mr Ahmadinejad said, according to the semi-official Fars news agency.

Hugo Chavez, the President of Venezuela who is an ally of Mr Ahmadinejad, added: "People are in the streets, some are dead, they have snipers, and behind this is the CIA, the imperial hand of European countries and the United States."

Mehdi Karroubi, a reformist cleric who was also a defeated candidate, was forced to cancel a religious ceremony today to mark the start of the three days of mourning for the 17 protesters officially acknowledged to have died during the crackdown. Reformists say that the true death toll is probably higher.

The Foreign Office is meanwhile investigating reports on Iranian state television that British passport holders are being arrested in Iran, but little official credence is being given to the reports.

The case of Jason Fowden, a journalist with dual British and Greek nationality who was arrested as he tried to leave Iran, is being handled by the Greek embassy in Tehran. It was felt that Greece stood a better chance of gaining a positive outcome for Mr Fowden, it is understood, because of anti-British feeling in Iran. The Iranian Foreign Minister has accused Britain of sending jumbo jet-loads of spies to disrupt the elections, and even Ayatollah Ali Khamenei, Iran's Supreme Leader, who until two weeks ago was regarded as above the political fray, has lambasted Britain as the "most treacherous" of the Western powers.

Although Iran's strategy appears to have succeeded in quietening unrest on the streets, cracks have appeared in Iran's clerical Establishment.

Mr Ahmadinejad hosted an election victory party last night to which he invited all of Iran's 290 MPs. Only 105 of them attended.

One of those who reportedly failed to appear was Parliament Speaker Ali Larijani, a high-profile figure and natural ally of Mr Ahmadinejad's who has been critical of some aspects of the Government's handling of the protests.

Ayatollah Hossein Ali Montazeri, the most senior dissident cleric in Iran and once the heir apparent of Ayatollah Ruhollah Khomeini, warned the authorities in a statement today that trying to snuff out dissent would prove to be futile.

If people were not allowed to voice their demands in peaceful gatherings, it "could destroy the foundation of any government," regardless of its power, he wrote. Ayatollah Montazeri fell out of favour with the ruling clerics by questioning their almost limitless powers.

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