Iran must come clean about its nuclear program and submit to increased inspections by a global monitoring body, a U.S. official told an international conference Monday.

"Despite professions of transparency and peaceful intent, Iran is going down the same path of denial and deception that handicapped international inspections in North Korea and Iraq," said John Wolf, U.S. assistant secretary of state for nonproliferation.

"We have seen the pattern of cheat and retreat before -- of begrudging compromises on process but obstinacy on real disclosure," Wolf said at the opening of a two-week meeting on the 1968 Nuclear Nonproliferation Treaty. The conference is one of the meetings that precedes a review of the 188-nation accord in 2005.

There was no immediate reaction to Wolf's remarks from Iran. In the past, Iranian officials have said they have nothing to hide because their nuclear program is only meant to generate electricity.

The United States has accused Iran, which is building a nuclear power plant in the southern part of the country, of having secret plans to produce nuclear weapons.

The International Atomic Energy Agency oversees compliance with the nonproliferation treaty. The head of the Vienna-based agency visited Iranian nuclear sites -- including a uranium mine -- in February and is expected to report to the agency's board in June.

Wolf said the agency should get tough in its probes of Iran's program.

"What is presented as 'compliance' may in fact not be real," he said. "The International Atomic Energy needs to ask the hard questions and get complete answers.

"It needs to go wherever necessary to find the truth and it needs to measure each answer against Iran's pattern to date of denial and deception," Wolf said.

Under the nonproliferation treaty, the declared nuclear powers of the 1960s -- the United States, China, France, Russia and Britain -- were meant to reduce their arsenals, try to stop the spread of nuclear weapons and ensure nuclear technology was only used for peaceful purposes. However, the accord has failed to stop the growth in the number of nuclear powers.