The newspaper said that during the demonstration, which took place in Vienna in mid-July, officials displayed selections from more than a thousand pages of Iranian computer simulations and accounts of experiments, saying they showed a long effort to design a nuclear warhead.

The Americans acknowledged that the documents do not prove that Iran has an atomic bomb, the report said.

But they presented them as the strongest evidence yet that the country is trying to develop a compact warhead to fit atop its Shahab missile, which can reach Israel and other countries in the Middle East.

The briefing for officials of the IAEA, including its director Mohamed ElBaradei, was a secret part of a US campaign to increase international pressure on Iran, The Times said.

But while the intelligence has sold well among countries like Britain, France and Germany, which reviewed the documents as long as a year ago, it has been a tougher sell with countries outside the inner circle, according to the report.

The computer contained studies for crucial features of a nuclear warhead, according to European and US officials who had examined the material, including a telltale sphere of detonators to trigger an atomic explosion, the paper said.

Nonetheless, doubts about the intelligence persist among some foreign analysts because US officials, citing the need to protect their source, have largely refused to provide details of the origins of the laptop computer beyond saying that they obtained it in mid-2004 from a longtime contact in Iran, according to The Times.

"I can fabricate that data," the paper quotes an unnamed senior European diplomat as saying of the documents. "It looks beautiful, but is open to doubt."

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