Mohammad Javad Zarif was quoted by Iran's Fars news agency after arriving in Vienna, where he was due to meet European Union foreign policy chief Catherine Ashton. U.S. Secretary of State John Kerry will join them on Wednesday.
Zarif's cautious optimism came a day after President Hassan Rouhani told Iranian television that a nuclear agreement was "certain" and that only "fine details" remained to be negotiated.
Talks between Iran and six powers - the United States, France, Germany, China, Russia and Britain - are due to conclude by a self-imposed Nov. 24 deadline with, diplomats hope, a deal to end a standoff that has lasted more than a decade.
Diplomats say major differences remain, especially over the future scope of Iran's enrichment of uranium, a process that can yield material either for civilian nuclear power stations - Tehran's stated goal - or for nuclear bombs, which Western powers have long suspected may be Tehran's underlying agenda.
Kerry said in Paris on Tuesday that he did not believe that reaching a lasting accord within six weeks was out of reach, although he noted that many issues remained to be resolved.
Asked about speculation that an extension will be needed beyond that deadline to nail down a permanent settlement with Iran, Kerry pointed out that he was headed for Vienna on Wednesday for three-way talks with Zarif and Ashton.
He dismissed doubters who spoke as if "they know more than I do" but insisted that "I'm not about to predict".
"I don’t believe it's out of reach," he said, but added, "We have some tough issues to resolve."
In a further sign of attempts to accelerate negotiations, Ashton's office said she and Zarif would meet with senior foreign ministry officials known as political directors of the six powers in the Austrian capital on Thursday, a day after the meeting between the top EU, U.S. and Iranian diplomats.
"The main thing for us now is that time is not being lost," Russian Deputy Foreign Minister Sergei Ryabkov was quoted as saying by Tass news agency.
Israel has threatened military force against Iranian atomic sites if diplomacy fails to ensure Iran is deprived of the means of developing nuclear weapons through enrichment. Iran says Israel's presumed atomic arsenal is the main threat to peace.
SIX WEEKS TO DEADLINE
A Western diplomat said the aim of Thursday's meeting would be to take stock of the status of the negotiations.
Ashton, who heads the team negotiating with Iran, will "work as hard as she can" to try and get a good agreement by the deadline, her spokesman, Michael Mann, said. "That is extremely important in every way."
One of Iran's chief negotiators, Deputy Foreign Minister Abbas Araqchi, last week raised the possibility that the talks could be extended. But a U.S. State Department official said Washington believed there was still time to reach a comprehensive solution by the target date.
Iran rejects Western allegations that it is seeking nuclear weapons capability, but has refused to halt uranium enrichment, and has been hit with U.S., EU and U.N. Security Council sanctions as a result.
"Although we do not expect a breakthrough in the trilateral negotiations (between Zarif, Ashton and Kerry) ... still this round could pave the way for a final agreement," Fars quoted Zarif as saying. "On the agenda is the volume of uranium enrichment and the timetable for lifting the sanctions."
Iran and the six powers last November reached an interim deal under which Tehran suspended its most sensitive nuclear activity in exchange for some easing of the sanctions.
(Additional reporting by Vladimir Soldatkin in Moscow, Louis Charbonneau in New York, John Irish and Matt Spetalnick in Paris, editing by Mark Heinrich)