UNITED NATIONS (AFP/Reuters) - Iranian President Mahmoud Ahmadinejad Thursday again cast 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. The United States led a mass walkout of the UN General Assembly when Ahmadinejad launched the 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. Ahmadinejad has in the past drawn uproar for his use of major speeches to call for the destruction of Israel and indicate that the US government may have been involved in 9/11. 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. 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: Would it not have been reasonable to bring to justice and openly bring to trial the main perpetrator of the incident in order to identify the elements behind the safe space provided for the invading aircraft to attack the twin World Trade Centre 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. Mr Ahmadinejad had a chance to address his own peoples 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. A French spokesman called Ahmadinejads attacks unacceptable, while the German delegation said it had left the assembly because of the crude, anti-American, anti-Israeli and anti-West tirade by the Iranian president. Ahmadinejad attacked Western powers for a catalog of misdeeds, but his address to the United Nations failed to mention Tehrans disputed nuclear program. Ahmadinejad said 'arrogant powers threatened anyone who questioned the Holocaust and the September 11 attacks on the United States with sanctions and military action. Ahmadinejad made only a passing reference to the Palestinian issue which has overshadowed this years UN General Assembly and did not comment on the Palestinian plan to ask the UN Security Council to recognise their nascent state. He accused the United States of using the 'mysterious September 11, 2001, attacks as a pretext to launch wars on Iraq and Afghanistan. The United States and its allies view Zionism as a sacred notion and ideology, the Iranian leader said. Ahmadinejads address also passed in silence over the pro-democracy uprisings that have swept the Arab world this year, including Syria, Irans closest Arab ally. US President Barack Obama told the United Nations on Wednesday that Iran and North Korea risked more pressure if they pursued nuclear programs that flouted international law. There is a future of greater opportunity for the people of these nations if their governments meet their obligations. But if they continue down a path that is outside international law, they must be met with greater pressure and isolation, he said.