Talks aimed at curbing Iran’s nuclear activity look set to run beyond Tuesday’s deadline for a deal.
Iran and the UN’s permanent five members plus Germany (P5+1) are involved in the negotiations, which are taking place in Vienna.
The aim is to agree limits on Tehran’s nuclear programme in return for international sanctions being relaxed.
How much access Tehran is prepared to grant to nuclear monitors is believed to be the stumbling block.
Iran’s Foreign Minister is flying back to Tehran from Vienna to consult directly with his government.