The Iranian leader repeated comments casting doubt on the origins of the Holocaust and the September 11, 2001 attacks and criticised the United States for killing Osama bin Laden rather than bringing him to trial.

European countries use the Holocaust as an excuse to pay "ransom to the Zionists", he said. The "diabolical" aims of the West are the cause of wars and the financial crisis, Ahmadinejad stormed.

In a repeat of walkouts at the United Nations and other international events in recent years, a US diplomat monitoring the speech in the UN General Assembly left halfway through the 20 minute discourse on Thursday.

The 27 European Union nations then followed in a coordinated protest move.

"Mr Ahmadinejad had a chance to address his own people's aspirations for freedom and dignity, but instead he again turned to abhorrent anti-Semitic slurs and despicable conspiracy theories," said US mission spokesman Mark Kornblau.

The German delegation said in a statement that it was protesting over the "crude, anti-American, anti-Israeli and anti-West tirade by the Iranian president".

And a French spokesman called Ahmadinejad's attacks "unacceptable".

The Iranian president caused a UN walkout last year when he alleged the US government could have been behind the September 11 attacks. He has also used speeches in the past to call for the destruction of Israel and cast doubt on the existence of the Holocaust.

Israel and Canada were among countries which had no diplomats in the assembly even for the start of Ahmadinejad's latest speech.

Ahmadinejad told the UN summit that the United States and its allies use the Western media to "threaten anyone who questions the Holocaust and the September 11 event with sanctions and military action".

Some European countries "still use the Holocaust, after six decades, as the excuse to pay fine(s) or ransom to the Zionists." The United States considered Zionism as "sacred" while they "allow sacrileges and insult" against other religions.

The Iranian leader said he had been threatened by the US government after he last year alleged American government involvement in the attacks and called for an independent investigation.

Moving to the US operation to kill bin Laden, Ahmadinejad said the al-Qaeda leader should have been brought to trial "in order to identify the elements behind the safe space provided for the invading aircraft to attack the twin World Trade Center towers".

In a general blast at the West, Ahmadinejad said: "Hypocrisy and deceit are allowed in order to secure their interests and imperialistic goal."

"Drug trafficking and killing of innocent human beings are also allowed in pursuit of such diabolic goals," he added.

"They weaken countries through military intervention and destroy their infrastructures, in order to plunder their resources by making them all the more dependent."

Western diplomats said they had expected a tough speech by Ahmadinejad and had prepared walkout plans in advance.