Ashton "is thinking about when to engage ministers as we move forward but no decisions have been made as yet. It would be an opportunity for them to take stock of where we are in the process," spokesman Michael Mann told AFP.
Yesterday Iranian news agency IRNA reported that foreign ministers from the five permanent members of the UN Security Council -- Ashton is the chief negotiator -- would arrive in Vienna later this week.
The talks, which began last week, are aimed at reaching a potentially historic accord under which Iran would reduce in scope its nuclear programme in order to kill off once and for all concerns that Tehran will one day get the bomb.
The deadline to reach an accord is July 20 when an interim accord struck in Geneva expires, although this can, if both sides agree, be extended by up to six months.
A senior US official said after the last round on June 20 that foreign ministers "may well" travel to Vienna.
She said this would happen when both sides have "reached the narrowing of the gaps to the place where very tough political decisions need to be made and need to be made at the level of a minister.