Iran's foreign minister headed to New York on Tuesday to resume nuclear talks with major powers but it was unclear if there would be a repeat visit by President Hassan Rouhani, who launched Tehran's opening a year ago.
Foreign Minister Mohammad Javad Zarif was to hold a working lunch with European Union foreign policy chief Catherine Ashton, the lead negotiator for the six powers, his deputy Abbas Araqchi said.
The two diplomats will set the terms for the relaunch of negotiations for a comprehensive deal on the future scope of Iran's nuclear programme to allay international concerns about its ambitions, Araqchi told state news agency IRNA.
The talks on Wednesday and Thursday will take place on the sidelines of the UN General Assembly, the same venue where in September last year Rouhani held a historic telephone call with President Barack Obama, overcoming more than three decades of estrangement between the two governments.
The honeymoon period after that call saw Tehran strike an interim deal with the six powers that gave it some relief from Western economic sanctions in return for scaling back its more sensitive nuclear activities.
But Iranian officials have sounded a more pessimistic note in recent days about the prospects for hammering out a comprehensive deal by a November 24 deadline.
- 'Disagreements serious' -
"The disagreements are serious," Araqchi said of the renewed negotiations after the two sides missed an earlier, July target date for a deal.
"We hope that after the discussions that we have had with the Americans, the Russians and the Chinese, and the talks we will have on Wednesday and Thursday, we will able to make progress," he said.
Another deputy foreign minister, Majid Takht-Ravanchi, sounded a similar note of caution after talks in Geneva last Thursday with the other three powers involved in the negotiations -- Britain, France and Germany.
"After two rounds of negotiations with the European representatives, our positions have not been reconciled and disagreements over serious questions still exist," Takht-Ravanchi said on Saturday.
The six powers, all of which except Germany sit on the UN Security Council and have nuclear weapons themselves, want Iran to scale back its atomic programme to ease fears the Islamic republic gets the bomb.
Tehran, which says its nuclear programme is exclusively for power generation and medical uses, in return wants painful European Union and US sanctions lifted.
The main stumbling block remains the size of Iran's capacity to enrich uranium, a process that can make fuel for peaceful nuclear uses but also the core of an atomic bomb.
Also at issue is the timeframe for the lifting of sanctions that Western governments regard as the essential lever that brought Tehran to the negotiating table after eight years of frequently strong rhetoric from Rouhani's predecessor Mahmoud Ahmadinejad.
Rouhani has yet to decide whether to travel to New York for the UN General Assembly, Iranian media said.
Ahmadinejad used the annual platform to issue regular diatribes against Israel that were a major element in the international isolation of Iran that Rouhani has vowed to end.