With little more than a day to reach an agreement, Iran is reportedly considering an extension of a nuclear talks deadline. Negotiations have faltered amid "serious gaps" between Western diplomats and Tehran.
Iranian sources said on Sunday that negotiators from Tehran were prepared to continue negotiations if no agreement had been struck by the evening with the United States, Russia, China, Britain, France and Germany, also known as the P5+1 group.
According to an anonymous source speaking to the Iranian students News Agency (ISNA), it would be "impossible to reach a final and comprehensive deal by (Monday) November 24."
The news agency AFP cited a separate anonymous source close to the Iranian team as saying that talks could continue for up to a year.
"We are still focused on agreeing to a kind of political agreement," the source said, adding: "That could be for a period of six months or a year. We must absolutely avoid a climate of confrontation with escalation from one side and the other."
Suggestions of prolonging the talks follow reports on Saturday evening in which both European and Iranian sources said that reaching the Monday deadline was unlikely.
"We're working hard," US Secretary of State John Kerry told reporters in Vienna late on Saturday, where he met with his Iranian counterpart Mohammed Javad Zarif for the fourth time in three days. "And we hope we're making careful progress, but we have big gaps, we still have some serious gaps, which we're working to close."
Western and Iranian diplomats reached an interim accord roughly one year ago. In February, they began negotiations which were supposed to be finalized by Monday.
At the heart of the high-level talks are the West's desire to hinder Iran's uranium enrichment capabilities - specifically, preventing Tehran from being able to produce atomic weapons - and Iran's desire for the West to end crippling economic sanctions. Iran contends its uranium enrichment program will be used only for energy production. However, the West has argued that intelligence information suggests the size of the program and Iranian research could be adapted for the production of weapons.
kms/tj (AP, AFP, Reuters)