An agreement that would open the door to a resolution of the decade-long nuclear standoff between Iran and six world powers is possible this week if negotiators exert the maximum efforts, Iran's foreign minister says.
But the Western side was more reserved on Thursday as it prepared for two days of talks in the Swiss city of Geneva over Iran's disputed nuclear programme.
The West and Israel suspect Iran's nuclear drive may be aimed at developing atomic weapons, but Iran insists the programme is only for the generation of electricity and medical purposes.
"If everyone tries their best, we may have one," Mohammad Javad Zarif, the foreign minister, said on Thursday after a breakfast meeting with Catherine Ashton, European Union foreign policy chief.
"We expect serious negotiations. It's possible," he said when asked if an agreement was conceivable.
"I believe it is even possible to reach that agreement this week," Zarif told France 24 television on Tuesday.
"But I can only talk for our side, I cannot talk for the other side."
Michael Mann, Ashton's spokesman, said the talks "are complex and have entered a serious phase".
Earlier on Thursday, Zarif admitted the talks - between Iran and the five permanent UN Security Council members and Germany - will be "very difficult".
"My colleagues and delegations from the P5+1 countries are starting very difficult negotiations because we have entered a detailed phase that is still difficult and precise," Zarif said on his Facebook page.
Wendy Sherman, lead US negotiator, has expressed hopes that the talks will be a "first step" to resolving the issue, and said that Washington is prepared to offer Iran "very limited, temporary, reversible" relief from sanctions.
Abbas Araghchi, Iran's senior negotiator and deputy foreign minister, has said that the fresh round of negotiations were "a test of the political will of the P5+1 to reach a solution" to end the nuclear crisis.
He was also expected to hold talks in Geneva with Lakhdar Brahimi, the UN-Arab League peace envoy to Syria, before travelling to Rome for a "few hours" to meet his Italian counterpart, Emma Bonino.