Iran is working on development and testing of a neutron initiator, a key final component of a nuclear weapon, The Times reported Monday.
The British newspaper claimed it had obtained confidential intelligence documents from "foreign intelligence agencies," and quoted a source at an "Asian intelligence agency" as confirming that Iran had been working on the device, the component of a nuclear bomb that triggers an explosion, "as recently as 2007."
A document cited by the paper also describes the use of uranium deuteride, a material experts believe has no possible civilian or military use other than in a nuclear bomb.
Pakistan, believed to have been the source of Iran's blueprints for a bomb, also uses uranium deuteride in its nuclear devices.
"Although Iran might claim that this work is for civil purposes, there is no civil application," David Albright, a physicist and president of the Institute for Science and International Security in Washington, was quoted by the Times as saying.
An Israeli government spokesperson reportedly told the paper that Israel was increasingly concerned about "the real intentions that may lie behind" Iran's nuclear program.
Iran insists its nuclear program is intended purely for the production of energy and medical technology.
Mark Fitzpatrick, senior fellow for non-proliferation at the International Institute for Strategic Studies in London, was quoted by the paper as saying: "The most shattering conclusion is that, if this was an effort that began in 2007, it could be a casus belli. If Iran is working on weapons, it means there is no diplomatic solution," he said, adding "Is this the smoking gun? That's the question people should be asking. It looks like the smoking gun. This is smoking uranium."