The proposal was thought to repeat an earlier demand to stop uranium enrichment and to shut down the Fordo underground enrichment facility.

In return, some of the sanctions which have been imposed on Iran could be eased, reports say.

Several rounds of sanctions have squeezed Iran's economy, with oil revenue slashed, the currency nose-diving in value and unemployment growing.

Reuters news agency quoted Mr Jalili as saying after the talks that there was "no justification" for shutting Fordo, although he said the issue of 20% enrichment "can be discussed in the negotiations... in a view of confidence-building".