Iran's President Mahmoud Ahmadinejad accused the West and Israel of nuclear "intimidation", after US President Barack Obama vowed to halt Tehran's alleged weapons program.
US and Israeli officials boycotted the Iranian's eighth annual address to the UN General Assembly, and there was no repeat of the walk-outs of previous years, but Ahmadinejad still had some harsh words for Tehran's foes.
"Arms race and intimidation by nuclear weapons and weapons of mass destruction by the hegemonic powers have become prevalent," he declared in a 35-minute speech that ended with a smattering of applause.
"Continued threats by the uncivilized Zionists to resort to military action against our great nation are a clear example of this bitter reality," he added, in his only reference to Israel.
Western powers believe that Iran's uranium enrichment program is tooled to produce enough fissile matter to arm a nuclear weapon that would upset the balance of power in an already volatile Middle East.
Iran insists it has a right to civilian nuclear research and has defied international economic sanctions and clear threats from Israel that it would launch a preemptive strike rather than see Tehran get the bomb.
On Tuesday, Obama reiterated the United States' stance in robust terms, declaring that America will "do what we must" to prevent Iran from passing the nuclear threshold -- increasing the chances of confrontation.
Foreign ministers from the United States, Russia, China, Britain, France and Germany will meet in New York on Thursday on the sidelines of the United Nations to discuss the increasingly tense nuclear showdown.
Ahmadinejad's last stay in New York as president has been marked as usual by new condemnation of Israel, which he refuses to mention by name, using the "uncultured Zionists" or a "fake regime" instead.
The United States boycotted the UN speech because of his attacks.
"We've seen Mr. Ahmadinejad once again use his trip to the UN not to address the legitimate aspirations of the Iranian people but to instead spout paranoid theories and repulsive slurs against Israel," said US spokeswoman Erin Pelton.
Israeli diplomats also stayed away, partly because their country is marking Yom Kippur, the holiest day of the Jewish calendars.
Outside the UN headquarters, demonstrators protesting at Ahmadinejad's presence set up a hangman's gallows to symbolize Iran's widespread executions.
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Diplomats from Britain, France and Germany sat through Ahmadinejad's address, but found nothing in his theological lecture to justify a repeat of the walkouts of previous years.
Israeli Prime Minister Benjamin Netanyahu was due to address the General Assembly on Thursday and call for tough action against Iran.
In past speeches, Ahmadinejad has said the US government may have had a role in the September 11, 2001 attacks on New York and called for the eradication of Israel. This time he lashed out at the West for the global economic crisis.
"Creation of worthless paper assets by using influence and control over the world's economic centers constitutes the greatest abuse of history, and is considered a major contributor to global economic crisis," he said.
But much of the speech was devoted to religion, and Ahmadinejad hailed the imminent arrival of an "Ultimate Savior."
Ahmadinejad said the savior is "a man who loves people and loves absolute justice, a man who is a perfect human being and is named Imam Al-Mahdi, a man who will come in the company of Jesus Christ and the righteous."
As a Shiite Muslim, Ahmadinejad reveres Islam's twelfth imam, Muhammad Al-Mahdi, who disappeared from the earth in the tenth century and is said to be due to return, accompanied by Jesus, to save mankind.
Ahmadinejad's speech received a smattering of applause and he acknowledged the acclaim with a wave before leaving the UN stage for the last time.
Another pariah, Zimbabwean leader Robert Mugabe, also lambasted the major powers, accusing the UN Security Council of an "insatiable appetite for war" and condemning NATO's campaign to topple Libya's Moamer Kadhafi.
Meanwhile, in a parallel meeting at the UN headquarters, West African and French leaders called for the United Nations to endorse a new regional military intervention force to help Mali recapture territory lost to Islamist rebels.
And Arab leaders discussed the crisis in Syria, after some of them called for an Arab peacekeeping force to intervene and protect Syrian civilians from Bashar al-Assad's beleaguered but still brutal regime.
British Prime Minister David Cameron said the blood of the children killed in Syria had become a "terrible stain" on the reputation of the United Nations.
And US Secretary of State Hillary Clinton appealed for the "paralyzed" UN Security Council to make a new attempt to end the conflict.