Iran is in talks with the United States and five other powers - Britain, China, France, Germany and Russia - on an agreement to curtail its nuclear program in exchange for relief from economic sanctions.

"We are coming to the end," said a senior Western diplomat, who added there was no plan to carry on for long past next Tuesday. "Either we get an agreement or we don't," he said, adding that the process "remains quite difficult".

Iranian Foreign Minister Mohammad Javad Zarif told Iranian state television that "a lot of progress has been made, but still various technical issues remain that need the other party's political will".

Still, all sides say a deal is within reach. U.S., European and Iranian officials, including U.S. Under Secretary of State Wendy Sherman and Iranian deputy foreign ministers Abbas Araqchi and Majid Takhteravanchi, held a six-hour negotiating session that ended at 3 a.m. on Friday, a senior U.S. official said.