In their excellent New York Times op-ed today, Gary Milhollin and Valerie Lincy write:

Having begun the Qum plant to supply a bomb’s fuel, wouldn’t Iran also create what’s needed to produce the rest of the bomb’s components? This means laboratories to perfect nuclear weapon detonation and workshops to produce the firing sets, high-explosive lenses and other necessary parts. Although there is plenty of suspicion that such sites exist, Iran has not admitted having them.

As if to answer, there’s this from the Financial Times today:

Iran ‘has secret nuclear arms plan’
Britain’s intelligence services say that Iran has been secretly designing a nuclear warhead “since late 2004 or early 2005″, an assessment that suggests Tehran has embarked on the final steps towards acquiring nuclear weapons capability.