World powers expect European Union foreign policy chief Catherine Ashton to lead nuclear negotiations with Iran in a four-month extension of the talks, even though she leaves her EU job in late October, said a senior western diplomat.

The diplomat spoke yesterday in Vienna hours after Iran and the six powers agreed to continue talking, after failing to meet a self-imposed July 20 deadline to reach an agreement on curbing the Iranian nuclear programme in exchange for ending sanctions.

Ashton's mandate as the EU's top foreign policy official expires at the end of October, before the new November 24 target date for a long-term settlement to end the decade-old dispute over Iran's nuclear programme.