International Atomic Energy Agency chief Mohamed ElBaradei also said Iran could be running close to 3,000 uranium-enriching centrifuges by the end of next month — a number that IAEA officials have described as the point of no return in the start of a large-scale program.

ElBaradei spoke at the end of a meeting of his agency's 35-nation board, a gathering that focused on Iran's refusal to heed U.N. Security Council demands that it freeze activities that could serve to make nuclear arms and provide answers on suspicious aspects of its program.

He also urged Iran to offer a "self-imposed moratorium" on enrichment, describing it as a "good confidence-building measure" that could launch negotiations on the standoff

But the chief Iranian envoy to the meeting asserted his country would never suspend enrichment — the key issue of Security Council concern. Iran has said its nuclear program is peaceful and aims to generate energy, not bombs.

Although they've called for a negotiated solution, both the U.S. and Israel have refused to outright dismiss the possibility that they might target Iran militarily if it refuses to back down.

ElBaradei described use of force as "an act of madness ... (that) would not resolve the issue."

"The next few months will be crucial," he said: "Iran is building a capacity, a knowledge" of enrichment that is irreversible, while not providing evidence sought by his agency "that this is a peaceful program."

"Even if Iran wants to have a weapon they are three to eight years away," ElBaradei said, citing unidentified intelligence sources for his estimate. But "the longer we delay, the less option we have to reach a peaceful solution."

Iran's defiance of U.N. Security Council demands it stop enrichment and construction of a plutonium-producing reactor as well as increase cooperation with IAEA inspectors has led to two sets of sanctions.

A recent IAEA report confirmed that Iran was expanding its activities and continuing to stonewall the IAEA in its attempts to gain more information on past activities of concern. That has set the stage for a new round of Security Council-imposed penalties.

Declaring that Tehran had become the "master of uranium enrichment" Ali Ashgar Soltanieh, Iran's chief IAEA envoy, said his country will never suspend its program.

Like enriched uranium, plutonium can be used for the fissile core of nuclear warheads. Iran, however, says it wants to develop enrichment to generate nuclear power and asserts it is building the plutonium-producing reactor for research and medical purposes.

Soltanieh evaded a question on whether his country had solved all technical problems in the intensely complicated enrichment process of spinning uranium gas through centrifuges at high speed.

U.S. officials have told The Associated Press their information indicates Iran has not yet achieved the technical perfection. The officials spoke on condition of anonymity because they were discussing confidential matters.

Gregory L. Schulte, the U.S. envoy to the IAEA, scoffed at Soltanieh's claim of enrichment mastery, telling AP Television News: "The Iranian ambassador spins faster than any centrifuge."

ElBaradei, however, cautioned that Iran was "speeding up its enrichment capacity" to the point where it could have just under 3,000 uranium-enriching centrifuges running in series by the end of July and "was steadily moving toward perfecting the technology."

"Whether some of the centrifuges are running with the speed desired, whether some of the centrifuges have been crashed, that is a part we have yet not seen and we still have to do some analysis," ElBaradei said.

"But it is clear ... that they are meeting their expectations at least in terms of the level of enrichment," he said, alluding to his agency's recent confirmation that centrifuges at Tehran's underground Natanz facility have churned out small amounts of fuel-grade enriched uranium.