Updated

The U.S. said Tuesday it will investigate a newspaper report that Iran is working on a trigger for a nuclear bomb, adding the "revelation" fueled concerns about the country's intentions.

State Department spokesman Philip Crowley's remarks appeared to give credence to a report in The Times of London stating it had obtained a secret document describing a four-year plan by Iran to test a neutron initiator, or bomb trigger

"There's been a public report about an issue related to... Iran's nuclear program. It's safe to say the United States government will be investigating those reports," Crowley told reporters.

The "revelation this week about nuclear triggers... all adds up to the fact that Iran has yet to really come to... the international community and address our concerns in a meaningful way," he continued.

When pressed to give his opinion of the news report, Crowley first replied, "no," before adding, "it was a fine piece of journalism. Enough said."

According to The Times report, the confidential notes from Iran's most sensitive military nuclear project date to early 2007, four years after Iran was thought to have suspended its weapons program.

An Asian intelligence source last week confirmed to the paper that his country also believed that weapons work was being carried out as recently as 2007 — specifically, work on a neutron initiator.

The technical document describes the use of a neutron source, uranium deuteride, which independent experts confirm has no possible civilian or military use other than in a nuclear weapon. Uranium deuteride is the material used in Pakistan’s bomb, from where Iran obtained its blueprint.

"Although Iran might claim that this work is for civil purposes, there is no civil application," said David Albright, a physicist and president of the Institute for Science and International Security in Washington, which has analysed hundreds of pages of documents related to the Iranian programme. "This is a very strong indicator of weapons work."

The documents have been seen by intelligence agencies from several Western countries, including Britain. A senior source at the International Atomic Energy Agency confirmed that they had been passed to the U.N.’s nuclear watchdog.

More on the secret document at The Times of London