He also spoke out against Israel for its "barbaric" attack on the Gaza Strip, "inhuman policies" in the Palestinian territories and what he called its domination of world political and economic affairs.
"How can crimes of the occupiers against defenceless women and children and destruction of their homes, farms, hospitals and schools be supported unconditionally by certain governments?"
Mahmoud Ahmadinejad, Iran's president
"How can crimes of the occupiers against defenceless women and children and destruction of their homes, farms, hospitals and schools be supported unconditionally by certain governments?
"It is no longer acceptable that a small minority would dominate the politics, economy and culture of major parts of the world by its complicated networks, and establish a new form of slavery, and harm the reputation of other nations, even European nations and the US, to attain its racist ambitions," he said.
Already speaking to a half-empty chamber, his attacks on Israel prompted walkouts by several delegations, including the US one.
Under increasing pressure over his country's nuclear programme, Ahmadinejad did not directly address the issue, calling only for the "eradication of arms race and elimination of all nuclear, chemical and biological weapons to pave the way for all nations to have access to advanced and peaceful technologies".
Moments before he spoke, foreign ministers of six global powers demanded Iran prepare a "serious response" by October 1 to demands it halt its nuclear programme or face serious consequences.
'Seize the opportunity'
Earlier in the day, Barack Obama, the US president, took Iran to task for its nuclear ambitions, warning that Tehran was running short of time and urging it to "seize the opportunity" at the talks with the five permanent UN Security Council members and Germany.
|Ahmadinejad has said he will not negotiate on Iran's right to enrich uranium [EPA]
Hillary Mann Leverett, who has worked with the US National Security Council and state department, told Al Jazeera that Ahmadinejad had "very forcefully" taken on Obama in his address.
"I think Ahmadinejad really put the issue of double standards on the table - double standards over nuclear, double standards over what he called 'military occupation'," she said.
The International Atomic Energy Agency says Iran has not been forthcoming about its nuclear programme and the UN Security Council has imposed sanctions against Iran three times since 2006 for its refusal to freeze uranium enrichment.
Tougher sanctions against Iran are being considered if the October 1 talks between the six powers and Iran do not yield results.
In a sign that Russian and the US could be moving closer on how to deal with Iran's nuclear programme, Moscow, which has stood in the way of stronger action against Tehran in the past, also came out on Wednesday to say Iran should not be allowed to develop nuclear weapons.
Dmitry Medvedev, the Russian president, also appeared to suggest that Moscow was moving closer to backing fresh sanctions against Iran, saying that while such tactics were rarely productive, "in some cases sanctions are inevitable".
"Our task is to maintain a system of incentives allowing Iran to use peaceful nuclear energy but [we] will not allow the creation of nuclear weapons," Medvedev said after meeting Obama on the sidelines of the UN General Assembly.
He added that the world should offer incentives "to help Iran make the right decision".
The US and its allies believe Iran is trying to produce nuclear weapons, while Tehran maintains that it is only building a peaceful nuclear energy programme.
Ahmadinejad has said he expects "free and open" discussions at the October 1 meeting but insists that Iran will not negotiate uranium enrichment.