Speaking at a news conference in New York, where he attended this week's opening of the UN General Assembly's new session, Rouhani said that after meetings between Iranian officials and the so-called P5+1 countries — Germany, China, Russia, the United States, Britain and France — the outlook is positive for some kind of deal.
"We hope that these talks would, in a short time, yield tangle results," he said through a translator.
"In speaking with senior European officials, and also hearing Mr. Obama, the president of the United States, it seemed that they sounded different than compared with the past, and I view that as a positive step in the settlement of the differences between the Islamic Republic of Iran and the West."
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Rouhani said his election in June, before coming to power in August, has created a "new environment," both within Iran but also globally, that is serving to "pave the way for better relations."
The news conference capped off a weeklong diplomatic push by the new Iranian administration to court Western countries, a marked departure from the standoffish stances taken by previous president Madmoud Ahmadinejad.
Rouhani has come across as a more moderate face of the hard-line clerical regime in Tehran and his pronouncements at the UN have raised guarded hopes that progress might be possible. But they have also served as a reminder that the path to that progress will not be quick or easy.
Any optimism was tempered by the caution expressed by Iran's own chief nuclear negotiator, who earlier Friday played down prospects for a quick breakthrough in talks with the United Nations nuclear agency over a stalled inquiry into Iran's atomic work.
During discussions in Vienna, home of the International Atomic Energy Agency, Iranian envoy Reza Najafi stressed the new government's policy of "constructive interaction" but also said he did not expect any agreement in the immediate future.
"This is the first meeting, so nobody, I guess, should expect that in just a one-day meeting we can solve [our] problems," Najafi, appointed as ambassador last month, told reporters as he arrived at the Iranian diplomatic mission.
"We expect to review the existing issues and also exchange views on the ways we can continue our co-operation to resolve all issues."
For the West, the IAEA negotiations are a test of any substantive shift by Iran from what it saw as intransigence under Ahmadinejad.
Chief IAEA inspector Herman Nackaerts used similar language to Najafi: "We are looking forward to discuss how we can intensify the dialogue to resolve all outstanding issues," he said.
For several years, the IAEA has been investigating suspicions that Iran may have co-ordinated efforts to process uranium, test explosives and revamp a ballistic missile cone in a way suitable for a nuclear warhead.
Iran says the allegations are baseless, but has pledged, since Rouhani took office in early August, to expand co-operation with the UN agency. Western diplomats have accused Iran of obstructing the IAEA investigation.
2 negotiation tracks
Separately, U.S. Secretary of State John Kerry met Iranian Foreign Minister Mohammad Javad Zarif in New York on Thursday, with both expressing cautious optimism.
The two sets of talks represent distinct diplomatic tracks but are linked because both centre on suspicions that Iran may be seeking the capability to assemble nuclear bombs behind the facade of a declared civilian atomic energy programme.
Iran says its programme is a peaceful bid to generate electricity. But its refusal to curb sensitive nuclear work and lack of full openness with IAEA inspectors have drawn tough Western sanctions, hurting its lifeline oil exports.
Rouhani said this week that Iran would never develop nuclear weapons and called for a nuclear deal in three to six months.
The IAEA has held 10 rounds of talks with Iran since early 2012 to try to resume its stalled inquiry into suspected atom bomb research.