Ahmadinejad urged "the suspension of members in the board of governors of the International Atomic Energy Agency, which use or threaten to use nuclear weapons".
"How can the United States be a member of the board of governors when it used nuclear weapons against Japan," he said.
He said nuclear atomic weapons were an encouragement to other countries to develop similar arsenals and called for a timetable for elimination of nuclear arms worldwide.
Alireza Ronaghi, Al Jazeera's correspondent in Tehran, said: "We have to be realistic about what he wanted to achieve.
"The walkouts were expected, they were announced before, he doesn't have any worries about the people who walked out, his message will come across and be heard despite the walkouts.
"The speech was less aggressive [than previous speeches].
"He is under enormous pressure from people in Iran, who accuse him of being too soft, to sign out of the Non-Proliferation Treaty.
"It is a difficult balancing act that he is trying to carry out."
Speaking from New York, Marwan Bishara, Al Jazeera's senior political analyst, said: "The US and Iran obsessionwith each other is paralysing the international community, is hindering the process from moving forward.
"There is a lot of dragging and there is a long way to go. Those who have the nuclear weapons are insensitive to those who do not have them.
"His [Ahmadinejad] message was that 'we are the victims, they [the nuclear powers] are the aggressors'.
"The forum is at risk of turning into a circus where the US and Iran attack each other while leaving the rest of the international community outside the cage."
Tehran has refused to abandon its enrichment programme and now faces the prospect of UN-backed sanctions as a result of its defiance in the face of international pressure.
Hillary Clinton, the US secretary of state, is set to address the assembly later on Monday.
She cautioned last week that any efforts to disrupt the talks will fail.
"If President Ahmadinejad wants to come and announce that Iran will abide by their non-proliferation requirements under the NPT, that would be very good news indeed," she said on Thursday
Clinton said if he tried to "divert attention from this very important global effort or cause confusion that might possibly throw into doubt what Iran has been up to ... I don't believe he will have a particularly receptive audience".
The month-long NPT review conference is held twice a decade to discuss the implementation of the treaty, which calls on signatories to abandon nuclear weapons and to prevent the spread of the technology.
Ban Ki-moon, the UN secretary-general, said over the weekend that more progress needs to be made in disarmament efforts, which have been boosted by new pledges from the US and Russia in recent months.
Ban also said Iran's and North Korea's nuclear programmes were "of serious
concern to global efforts to curb nuclear proliferation".