Iran says it has begun using new advanced centrifuges to enrich uranium - the latest step in reducing its commitment to a 2015 nuclear deal with world powers. Forty such centrifuges were now operational, said nuclear agency spokesman Behruz Kamalvandi. Enriched uranium can be used to make reactor fuel but also nuclear weapons. Iran stopped abiding by two commitments in July in response to sanctions the US reinstated when it abandoned the deal. President Donald Trump wants to force Iran to negotiate a new agreement that would place indefinite curbs on its nuclear programme and also halt its development of ballistic missiles. But Iran has so far refused. Other countries which are parties to the deal - the UK, France, Germany, China and Russia - have tried to keep it alive. But the sanctions have caused Iran's oil exports to collapse, the value of its currency to plummet, and sent its inflation rate soaring. The 2015 deal was designed to prevent Iran developing nuclear weapons, though Iran has always denied wanting to do so.