The Bush administration confirmed on Wednesday that it would send a top diplomat to a meeting with a senior Iranian negotiator this weekend – a US policy shift that European diplomats hope will encourage more flexibility from Tehran over its disputed nuclear programme.

William Burns, a US under-secretary of state, will join European, Russian and Chinese envoys and Javier Solana, the European Union foreign policy chief, in a meeting in Geneva on Saturday with Saeed Jalili, secretary of Iran’s supreme national security council.