UNITED NATIONS (AP) -- Iranian President Mahmoud Ahmadinejad on Monday rejected allegations his country is developing nuclear weapons, citing "not a single credible proof."
In the first day of a monthlong conference reviewing the Nuclear Nonproliferation Treaty, the Iranian leader dismissed allegations that his country's uranium enrichment program is designed to produce a bomb, prompting the United States and other nations to call for sanctions.
Mr. Ahmadinejad also chided the United States for refusing to rule out the use of nuclear weapons. He invited President Obama to join a "humane movement" that would set a timetable for abolishing nuclear arms everywhere.
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"Regrettably, the government of the United States has not only used nuclear weapons, but also continues to threaten to use such weapons against other countries, including Iran," Mr. Ahmadinejad said.
He referred to the new U.S. Nuclear Posture Review's provision retaining an option to use U.S. atomic arms against countries not in compliance with the nonproliferation pact, a charge Washington lays against Iran.
As the Iranian president spoke, the U.S. delegation of working-level staff walked out of the General Assembly hall. Mr. Ahmadinejad is the only head of state participating in the conference.
Secretary of State Hillary Rodham Clinton, scheduled to follow Mr. Ahmadinejad to the U.N. stage later Monday, suggested over the weekend he was coming to New York "to divert attention and confuse the issue."
"We're not going to permit Iran to try to change the story from their failure to comply" with the NPT, she said on Sunday's "Meet the Press" on NBC.
Opening the conference, U.N. Secretary-General Ban Ki-moon directly challenged Tehran.
"The onus is on Iran to clarify the doubts and concerns about its program," the U.N. chief told the delegates from 189 nations.
He called on the Tehran government "to fully comply with Security Council resolutions" demanding that it halt enrichment, which Washington and others contend is meant to produce the nuclear fuel for bombs in violation of Iran's NPT obligations.
While delegates assess the state of the NPT in U.N. conference halls, American and European diplomats will be working elsewhere to reach agreement with the sometimes reluctant China and Russia on a fourth round of U.N. Security Council economic penalties to impose on Iran.
Although Mr. Ahmadinejad's presence meant the first-day agenda was dominated by the Iran issue, it was only the beginning of a four-week diplomatic marathon meant to produce a consensus final document pointing toward ways to better achieve the NPT's goals of checking the spread of nuclear weapons, while working toward reducing and eventually eliminating them.
The treaty is regarded as the world's single most important pact on nuclear arms, credited with preventing their proliferation to dozens of nations since it entered into force in 1970. It was a grand global bargain: Nations without nuclear weapons committed not to acquire them, those with them committed to move toward their elimination, and all endorsed everyone's right to develop peaceful nuclear energy.
The 189 treaty members gather every five years to discuss new approaches to problems, by agreeing, for example, that the International Atomic Energy Agency, the U.N. nuclear inspection agency, should be strengthened. The only countries that are not treaty members are India, Pakistan, North Korea -- all of which have nuclear arsenals or weapons programs -- and Israel, which has an unacknowledged nuclear arsenal.
But the NPT conference cannot easily "name and shame" an alleged treaty violator, such as Iran, since as a member state its delegation would block consensus.
At three of seven past conferences, delegates failed to produce a declaration, including in 2005, at a time when the U.S. administration, under President George W. Bush, was unenthusiastic about arms control talks.
Mr. Obama has steered the United States back onto a negotiating track, including with a new U.S.-Russian agreement to reduce their thousands of long-range nuclear arms.
Despite that, Libran N. Cabactulan, the Philippine diplomat who is president of this 2010 NPT conference, said he finds the No. 1 goal of many treaty nations is to press the NPT nuclear powers -- also including Britain, France and China -- to move more rapidly toward disarmament.
In his opening remarks, the Mr. Ban listed "real gains for disarmament" as his first "benchmark for success."
To that end, the Nonaligned Movement of 118 developing nations has submitted to the conference a detailed "plan of action" for moving toward global nuclear disarmament by 2030. One its earliest steps is full ratification and entry into force of the 1996 treaty banning all nuclear tests.
In the first concrete step associated with this 2010 meeting, Indonesia announced last week it would ratify the test-ban treaty. Mr. Obama has pledged to push for U.S. ratification of the pact, which was rejected by the Republican majority in the U.S. Senate in 1999.