President Mahmoud Ahmadinejad ordered Iran's atomic chief on Sunday to enrich uranium to 20 percent, in a fresh challenge to Western powers bidding to rein in Tehran's galloping nuclear drive.

"I had said let us give them (world powers) two to three months and if they don't agree, we would start ourselves," Ahmadinejad said in a speech at an exhibition on laser technology which was broadcast live on state television.

"Now Dr (Ali Akbar) Salehi, start to make the 20 percent with the centrifuges," the hardliner told the atomic chief, who was sitting in the audience.