The Islamic Republic has seldom seen such scenes. President Ahmadinejad had to cut short an interview on state-controlled television because chants of “Ahmadi! Ahmadi! Resign! Resign!” could clearly be heard in the background.

After two quiescent summer months, huge new protests erupted across Iran yesterday, with popular anger at the alleged theft of June’s presidential election inflamed by the subsequent killing, torture, rape and show trials of opponents of the regime.

Mir Hossein Mousavi, 68, the former Prime Minister and de facto opposition leader, had to abandon plans to join the huge anti-government demonstrations in Tehran when hardliners attacked him and his car.

Ayatollah Khatami, 65, a popular former President who supports the opposition, was knocked to the ground, had his robe ripped and lost his cleric’s turban — a black garment signifying that he is a sayyid, or descendant of the Prophet.

In Tehran and other cities, tens of thousands of demonstrators hijacked Iran’s annual al-Quds Day rallies in support of the Palestinian cause and turned them into protests against the oppression of Iranians. The security forces hit back with teargas and baton charges. There were violent confrontations between government and opposition supporters in the squares and avenues of central Tehran and numerous reports of arrests and injuries.

In an address to the Friday prayers gathering in Tehran, Mr Ahmadinejad caused international outrage by again dismissing the Holocaust as a myth and claiming that the regime in Israel was collapsing. Yesterday’s turmoil, however, suggested that his regime was the one in trouble.

There had been no major demonstrations since July 17 but the Government could hardly cancel al-Quds Day, an event initiated by Ayatollah Khomeini, the founder of the Islamic Republic, and the opposition seized its chance. Its supporters turned out in huge numbers and paralysed the centre of Tehran; estimates of the turnout ranged from 100,000 to 500,000. They were young and old, male and female, rich and poor, and came with green wristbands, T-shirts, balloons and banners to show support for Mr Mousavi’s green movement.

Car drivers stuck in the gridlock sounded their horns and turned on their headlights to show support. Protests were also reported in Isfahan, Shiraz, Tabriz, Qum, Rasht and other cities. Within hours the internet was flooded with video clips showing jubilant crowds applauding, singing and holding their arms aloft to form a sea of V-for-victory signs. Witnesses said that they chanted “Rape and torture will not stop us” and “Liar, liar, where is your 63 per cent?” — a reference to Mr Ahmadinejad’s alleged share of June’s vote.

They chanted: “I will fight, I will die, but I will take back my country”, and “Supreme Leader! This is the last message — the Green Movement of Iran is prepared for the uprising”. Mocking the regime’s concern for the Palestinians, they chanted: “Neither Gaza nor Lebanon — I sacrifice my life for Iran.” Some held placards saying: “If I rise, if you rise, everyone will rise.”

One elderly woman said: “They have raped, murdered and tortured our youth after stealing the election. May God’s wrath come down on them.”

A 69-year-old merchant said: “I came to show solidarity with the youth of my country. The regime is destroying Islam and Iran.”

A young female student said: “The cheating, the raping, the killing and the torture drive you mad. I’ve come to express my hatred for Ahmadinejad and his protector, that so-called Great Leader of the Revolution.”

The Revolutionary Guards had warned that demonstrations would be crushed and the security forces responded with baton charges, teargas and pepper gas, but there were reports of protesters hurling stones and beating pro-government basiji militiamen.

The security forces also cordoned off Tehran University, where Mr Ahmadinejad addressed thousands of government supporters bussed in for Friday prayers. Ali Akbar Hashemi Rafsanjani, the former President, had addressed Friday prayers on al-Quds Day for most of the past quarter century, but was barred yesterday because of his opposition sympathies.

Mr Ahmadinejad used the occasion to deliver another verbal onslaught on Israel, saying that the Holocaust — the West’s “pretext” for creating the Zionist state — was “a lie based on an unprovable and mythical claim”.

He said that confronting Israel was a “national and religious duty” and warned Israel’s supporters: “This regime’s days are numbered. It is on its way to collapse. It is dying.”

Mr Ahmadinejad was speaking just days before his scheduled address to the UN General Assembly and his words provoked outrage abroad. David Miliband, the British Foreign Secretary, called his comments abhorrent. The White House issued a condemnation. The World Jewish Congress urged UN member states to boycott his speech.

Yesterday’s protests show that the Iranian regime is still far from secure and that, with summer over, its problems will mount. The football season has begun, meaning large and volatile crowds will gather each weekend. At the same time students, who are traditionally in the vanguard of Iranian protest movements, are pouring back into the capital for the start of the new academic year next week.

There are rumours that the regime may shut down some universities for a term. It is said to be purging “suspect” teachers and increasing the number of pro-government basiji volunteers in schools and colleges. In recent weeks the regime has cancelled other public events, including the commemoration of Imam Ali’s death at the mausoleum of Ayatollah Khomeini. During August it is understood to have moved three big football matches out of Tehran or had them played behind closed doors.