Iran on Tuesday began enriching uranium to 20 per cent purity level at its Natanz plant in defiance of world powers but under the supervision of inspectors from the UN nuclear watchdog, state media said. Al-Alam television quoted a source from Iran's atomic body as telling the state-owned channel that Iran has started enriching uranium to 20 per cent in the presence of IAEA (International Atomic Energy Agency) inspectors at Natanz. The United States and France said on Monday they will push for strong new UN anti-nuclear sanctions against Iran after Tehran announced it was going to step up its uranium enrichment.