UNITED NATIONS — President Mahmoud Ahmadinejad of Iran said Tuesday that relations with the United States might never be repaired if new sanctions were imposed against his country, that the United Nations atomic agency had no authority to poke its nose into matters like missiles and that despite his contested re-election last year, Iran had not become a republic of fear.
While Tehran has been generally opposed to improving relations with Washington, maintaining its hostility as a cornerstone of the Islamic revolution of 1979, Mr. Ahmadinejad suggested that the Obama administration was the last hope for the United States.
“Mr. Obama is the biggest and last opportunity that the United States has to improve its image in the world,” he said in a 40-minute interview. “If this opportunity is not used well, it will not present itself again.”
Later in the day, he suggested that relations with Tehran might never recover from a United States push for new economic and military sanctions against Iran through the United Nations Security Council. New penalties would “mean relations between Iran and the U.S. will never be improved again,” Mr. Ahmadinejad said at a news conference.
Iran faces a fourth round of Security Council sanctions being negotiated now over its lack of cooperation on its nuclear program, but Mr. Ahmadinejad maintained that his country would be able to withstand any new sanctions, as it had in the past.
He accused the International Atomic Energy Agency of wandering well outside its mandate in raising questions about missile design and other military matters.
“The agency has no right to intervene in the missile program of any country,” Mr. Ahmadinejad said in the interview. “What does that have to do with the purview of the agency?” he added, calling it another “imperfection” in the nuclear nonproliferation treaty.
Yukiya Amano, the director general of the I.A.E.A., told the opening session of the nuclear nonproliferation treaty review conference here on Monday that his agency “remains unable to confirm that all nuclear material is in peaceful activities because Iran has not provided the necessary cooperation.”
A February report from his agency said that Iran needed to “clarify the production of nuclear related equipment and components by companies related to the defense industry.” Among the outstanding questions was one about engineering design and computer modeling of the payload chamber for missiles.
“The N.P.T. does not mention missiles,” said Mr. Ahmadinejad, making a rare appearance by a head of state at the nuclear treaty review conference held every five years. “That is a separate subject.”
Foreign ministers and other senior diplomats had voiced concern that the Iran issue would dominate the monthlong negotiations, but they said the conference was quickly focusing on the three main pillars of the 40-year-old treaty: arms cuts, nonproliferation of nuclear weapons and the civilian uses of nuclear power.
Negotiators noted with satisfaction that Indonesia had announced that it would seek ratification of the Comprehensive Test Ban Treaty. Indonesia is one of the key countries with a nuclear program needed for the treaty to go into affect.
On issues away from the conference, Mr. Ahmadinejad denied that a crackdown on anti-government protestors had engendered fear or that it had pushed Iranians to flee the country.
“Who is afraid inside Iran?” he said, calling support for the Islamic revolution stronger than it has been in a decade.
With regard to three young American hikers jailed in Iran, Mr. Ahmadinejad repeated his position that he would like to see them free, as well as some seven Iranians he said were incarcerated in the United States. “We are working to release all of the prisoners,” he said. The future of the Americans, he said, was up to the courts.
Family members of the three Americans — Sarah E. Shourd, Shane M. Bauer and Joshua F. Fattal — maintain that they crossed the Iranian frontier by accident while hiking in Kurdistan last summer.
Mr. Ahmadinejad took a slightly harder line on the question of Robert Levinson, a former F.B.I. agent who disappeared while on a business trip to Iran three years ago.
“We were told that he was an official representative of the U.S. government, that he was an F.B.I agent,” said Mr. Ahmadinejad, raising the question of what Mr. Levinson might have been doing on Kish Island in the Persian Gulf while not confirming that Iran knew his whereabouts.
“It is generally hard to predict the activities and whereabouts of intelligence officers. They can be in a hundred different places in the world in a very short period of time.”