"Iran and the P5+1 (major world powers) are very serious on resolving the remaining disputes by November ... but everything including an extension is possible if we cannot reach an agreement," Iran's top negotiator, Abbas Araqchi was quoted as saying on Friday by the semi-official Fars news agency, in the first hint an extension was being contemplated.
Iran and the six -- the United States, France, Germany, China, Russia and Britain -- hope that resolving the more-than-decade-long nuclear standoff with Iran will reduce regional tensions and alleviate the risk of another war in the Middle East. Israel has repeatedly threatened to use military force against Iranian atomic sites if diplomacy fails to defuse the standoff.
Iran rejects allegations from Western powers and their allies that it is seeking a nuclear weapons capability, but has refused to halt uranium enrichment, and been hit with U.S., European Union and U.N. Security Council sanctions as a result.
Top diplomats of the United States, Iran and the European Union will meet in Vienna next week to work on a comprehensive deal ahead of a Nov. 24 deadline, aimed at curbing Tehran's sensitive nuclear activities in exchange for gradually lifting sanctions against Iran.
"Iran and Western powers are very determined and serious to reach a result. Issues like enrichment and lifting of sanctions will be discussed in Vienna," Araqchi said.
"We are still optimistic about meeting the deadline."
Iranian and Western diplomats say significant differences remain over the future scope of Iran's uranium enrichment activity. Enrichment is a process of purifying uranium for use as fuel for power plants or, if enriched to a very high purity, for bombs.
A series of meetings have been held since early this year to try to narrow the gaps. A U.S. State Department spokeswoman said this week Washington still believed a deal was possible by the agreed target date.
In addition to enrichment, the speed of lifting sanctions is another sticking point, one on which Iranian and Western delegations have sharp differences.
The United States and Europeans are prepared to lift their unilateral sanctions very quickly in the event of an acceptable agreement, Western diplomats say, but U.N. measures would be ended gradually based on Iran's compliance with any future deal.
Araqchi hoped that substantial progress could be made in narrowing disagreements when Iran and the six powers meet next week. "If we cannot reach adequate results this time (in Vienna) we will surely miss the (November) deadline," Araqchi said. "Therefore, The West (P5+1) should use this opportunity and find proper solutions."
Some analysts believe meeting the deadline is impossible.
"It's become increasingly clear that a deal will not be struck by the 24 November deadline," said Mark Fitzpatrick, director of the non-proliferation program at the International Institute for Strategic Studies (IISS) think-tank.
"But rather than a return to more sanctions and more centrifuges, another extension of the interim deal is the best fall-back alternative for both sides. Iranian officials are wise to start preparing their public for this outcome."
Last year in Geneva, Iran and the six powers reached an interim agreement under which Tehran won some easing of sanctions in return for halting its most sensitive nuclear work.
But they failed to meet a July 20 target for a comprehensive agreement and they sat a new deadline of Nov. 24.
"Reaching a full-fledged agreement by 24 November no longer appears possible. What is possible is a breakthrough that could justify adding more time to the diplomatic clock," said Iran analyst Ali Vaez of the International Crisis Group think-tank.