The United States led a mass walkout of the UN General Assembly this evening when Iran's President Mahmoud Ahmadinejad launched an outspoken attack on Western nations.

A US diplomat who was in the assembly hall to monitor the speech left halfway through, while the 27 European Union nations then followed in a coordinated protest move.

Without naming any country, the Iranian leader strongly attacked the role of the United States and its allies in wars and the financial crisis and called on major powers to pay reparations for slavery.

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

He then went on to describe the 9/11 attacks as 'a mysterious incident' which was used to spark war in Afghanistan.

"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.

"It was a coordinated position by the EU if the Iranian president called into question European nations for their 'support of Zionism' and made reference to the Holocaust," a French source told AFP.