Iran has removed the seals on its uranium-enrichment plant at Natanz and says it will resume research on nuclear fuel, ending a two-year voluntary suspension, despite warnings from western Europe, Russia and America. The prospect of some form of sanctions against Iran, either agreed at the United Nations or imposed unilaterally by western countries, is growing. But Iran's president, Mahmoud Ahmadinejad, seems set on a showdown. (economist)