"When we were negotiating with the Europeans in Tehran, we were still installing some of the equipment at the Isfahan site. There was plenty of work to be done to complete the site and finish the work there. In reality, by creating a tame situation, we could finish Isfahan," said Hassan Rowhani, who headed talks with Britain, France and Germany until last year.

"From the outset, the Americans kept telling the Europeans, 'The Iranians are lying and deceiving you, and they have not told you everything.' The Europeans used to respond, 'We trust them,'" Mr. Rowhani said in a speech to the Supreme Council of Cultural Revolution.

The speech, which lays out Iran's policy of nuclear deception in unprecedented detail, was published in an Iranian journal that circulates among the nation's ruling elite.

He described the regime's quandary in September 2003 when the International Atomic Energy Agency demanded a "complete picture" of its nuclear activities.

"The dilemma was if we offered a complete picture, the picture itself could lead us to the U.N. Security Council," he said. "And not providing a complete picture would also be a violation of the resolution, and we could have been referred to the Security Council for not implementing the resolution."

Iran successfully hid a vast nuclear-weapons research effort for nearly two decades.

Mr. Rowhani's remarks were disclosed at an awkward moment for the Iranian government, ahead of a meeting tomorrow of the United Nations' atomic watchdog, which must make a fresh assessment of Iran's banned nuclear operations...