"We believe we can reach an agreement and we have come here with the political will to reach a final agreement," Zarif said late on Monday after meeting EU Foreign Policy chief Catherine Ashton in Vienna. (Agencies)
"If all sides enter the talks with the political will to resolve the issue, we will be able to reach positive results but it will take time," he added in statements carried by a state news agency.
Three days of talks open on Tuesday in Vienna between Iran and P5+1 group of nations - Britain, China, France, Russia, United States and Germany.
Building on an interim deal reached in November, the negotiations will seek a comprehensive accord that will once and for all allay Western suspicions that Iran's nuclear programme masks military objectives, a claim denied by Iran.
"Our objective is to provide the guarantee in the negotiations that Iran's nuclear programme will remain peaceful," Zarif said after a working dinner with Ashton who represents P5+1.
His remarks came a day after supreme leader Ayatollah Ali Khamenei said the nuclear talks with world powers would "lead nowhere" but that he did not oppose them.
"I repeat it again that I am not optimistic about the negotiations and they will lead nowhere, but I am not against them," said Khamenei.
Iran began implementing in January the landmark November deal under which it agreed to freeze some nuclear activities for six months in exchange for modest sanctions relief.
Under the ‘comprehensive’ deal now being sought, the powers will want Iran to scale back its activities permanently.
"We believe we can reach an agreement and we have come here with the political will to reach a final agreement," Zarif said late on Monday after meeting EU Foreign Policy chief Catherine Ashton in Vienna.