Countries keep their nuclear programs secret. That makes Iran’s trumpeting every new stage of warhead development suspicious.
If Iran wanted to fend off the impeding strike on its nuclear facilities, it would say the bomb is ready. Nobody could definitely disprove that, and the strike would be recalled for fear of retaliation.
Is Ahmadinejad inviting a strike, pleading for one? A nuclear program is fairly expensive, and the Iranian budget is tight. Iranians might or might not have the nuclear know-how. It is not impossible that Ahmadinejad wants an attack to cover a failed nuclear program.
Iranians actually accepted similar excuse—the accidental downing of an Iranian civil plane by the Americans—to end the war with Iraq.
That said, the Iranian facilities still must be bombed; we shouldn’t take chances with nuclear weapons.