China really wants to look good for the Olympics so with recent problems in Tibet, China dumped a whole bunch of new info about Iran's nuclear program onto the table at the UN:

Beijing is believed to have decided to assist the inspectors after documents seized from Iranian officials included blueprints for "shaping" uranium metal into warheads, the testing of high explosives used to detonate radioactive material and the procurement of dual-use technology.

Much of the new material was presented to the governors of the Vienna-based IAEA in February. That meeting is said to have triggered China's change of heart.
Change of heart my hairy ass.