Shahram Amiri returned to Tehran early on Thursday, saying he was pressured to lie about Iran’s nuclear program. Washington denied kidnapping Amiri and insisted he had lived freely in the United States.

Officials said the scientist described to US intelligence officers details of how a university in Tehran became the covert headquarters for Iran’s nuclear efforts, the newspaper reported.

While still in Iran, he was also one of the sources for a much-disputed National Intelligence Estimate on Iran’s suspected weapons program, published in 2007, the officials were cited as saying.

One official said Amiri provided “significant, original” information about secret aspects of his country’s nuclear program, the newspaper said.