Talks between Iranian negotiators and the six world powers on Iran's nuclear programme are going into a second day in the Turkish city of Istanbul after the two sides gave widely differing accounts of their discussions. After the first session, the Iranian team said the talks took place in a positive atmosphere. But after a second meeting, one western diplomat said his side had been very angry and frustrated by Iran's behaviour. Western powers have accused Iran of developing a nuclear bomb, but Iran insists that its programme is for peaceful purposes.