Instead, he said, Iran has decided to pursue the monitoring of its nuclear program "through its appropriate legal path," the International Atomic Energy Agency, which is the U.N.'s nuclear watchdog.
When Ahmadinejad was ushered to the podium of the U.N. General Assembly to speak, the U.S. delegation walked out, leaving only a low-ranking note-taker to listen to his speech.
The Iranian leader spoke hours after French President Nicolas Sarkozy warned the assembly that allowing Iran to arm itself with nuclear weapons would be an "unacceptable risk to stability in the region and in the world."
Earlier, German Chancellor Angela Merkel threatened tougher sanctions against Iran if the country remains intractable on the dispute over its nuclear program.
Iran insists that its nuclear program is purely peaceful and aimed solely at producing nuclear energy. But the United States and key European nations believe the program is a cover for Iran's real ambition: producing nuclear weapons.
Ahmadinejad has defied two Security Council resolutions demanding that it suspend its uranium enrichment program and imposing escalating sanctions against key figures and organizations involved in the nuclear program. He made clear in his speech that Iran does not intend to comply with them now.
"In the last two years, abusing the Security Council, the arrogant powers have repeatedly accused Iran and even made military threats and imposed illegal sanctions against it," the Iranian leader said.
"Fortunately, the IAEA has recently tried to regain its legal role as support of the rights of its members while supervising nuclear activities," he said. "We see this as a correct approach adopted by the agency."
"Previously, they illegally insisted on politicizing the Iranian nation's nuclear case, but today, because of the resistance of the Iranian nation, the issue is back to the agency, and I officially announce that in our opinion the nuclear issue of Iran is now closed and has turned into an ordinary agency matter," Ahmadinejad said.
Congress signaled its disapproval of the Iranian president with a vote Tuesday to tighten sanctions against his government and a call to designate his army a terrorist group.
The swift rebuke was a rare display of bipartisan cooperation in a Congress bitterly divided on the Iraq war. It reflected lawmakers' long-standing nervousness about Tehran's intentions in the region, particularly toward Israel - a sentiment fueled by the pro-Israeli lobby whose influence reaches across party lines in Congress.
"Iran faces a choice between a very big carrot and a very sharp stick," said Rep. Tom Lantos, chairman of the House Foreign Affairs Committee. "It is my hope that they will take the carrot. But today, we are putting the stick in place."
The House passed, by a 397-16 vote, a proposal by Lantos, D-Calif., aimed at blocking foreign investment in Iran, in particular its lucrative energy sector. The bill would specifically bar the president from waiving U.S. sanctions.
Current law imposes sanctions against any foreign company that invests $20 million or more in Iran's energy industry, although the U.S. has waived or ignored sanction laws in exchange for European support on nonproliferation issues.
In the Senate, Joseph Lieberman, I-Conn., and Jon Kyl, R-Ariz., proposed a nonbinding resolution urging the State Department to label Iran's military - the Islamic Revolutionary Guard Corps - a terrorist organization.
The Bush administration had already been planning to blacklist a unit within the Revolutionary Guard, subjecting part of the vast military operation to financial sanctions.
Lantos' bill was expected to draw criticism from U.S. allies in Europe. During a visit to Washington last week, French Foreign Minister Bernard Kouchner told lawmakers that France opposes any U.S. legislation that would target European countries operating in Iran. He argued that such sanctions could undermine cooperation on dealing with Iran.