No concrete evidence to support that argument.
Iran admits it. They need to enrich uranium to make nuclear fuel. The question is whether or not they're going to manufacture weapons-grade materials.
That's why the West offers them nuclear fuel. So that they have no excuse to enrich uranium.
As a bit of an aside, did anyone else notice that Kerry got reamed by the GOP for being a soft liberal when he suggested giving them nuclear fuel, and now the Bush Administration has run with the idea?