The two days of talks in Geneva, Switzerland, were "substantive and forward-looking," said a rare joint statement from Iranian Foreign Minister Javad Zarif and European Union foreign policy chief Catherine Ashton, the lead negotiator with Iran.
The statement, which can be found at tinyurl.com/UPI-Joint-Statement, set the next meeting for Geneva Nov. 7-8.
It said a plan Zarif presented was "a proposed basis for negotiation, which is being carefully considered ... as an important contribution."
Sanctions experts from the two sides are to meet before the next talks start.
"I've been doing this now for about two years, and I have never had such intense, detailed, straightforward, candid conversations with the Iranian delegation before," a senior Obama administration official told reporters at the conclusion of the meeting between Iran and the five permanent U.N. Security Council members -- the United States, Russia, China, Britain and France -- and Germany.
"There is more work -- much more work -- to do, as we knew there would be," said the official, who declined to be identified under the diplomatic protocol for briefing reporters.
"Any agreement has to give the United States and the world every confidence that Iran will not acquire a nuclear weapon," the official said.
Zarif told reporters, "We have had two days of extensive and fruitful consultations ... which will hopefully be the beginning of a new phase in our relations."
He said Iran's goal was "to give confidence about the peaceful nature of the Iranian nuclear program."
"There is no reason to be worried about it," Zarif said, while reiterating Iran would not give up its right to nuclear energy.
Russian Deputy Foreign Minister Sergei Ryabkov was more reticent in describing the talks. He told Russian non-governmental news agency Interfax the two sides were still "kilometers apart" and said the talks were "difficult, at times tense, at times unpredictable."
The two sides said they agreed not to provide details of Iran's proposal or of the negotiations.
This made it unclear whether Iran moved closer to accepting immediate curbs to its nuclear program, which it says is for peaceful civilian purposes but the United States and other countries allege is aimed at acquiring a nuclear weapons capability.
It was also unclear whether Washington and other Western powers were any closer to lifting crippling economic sanctions against Iran in exchange for Tehran's concessions.
Unlike in previous negotiations, Zarif spoke in English during the P5-plus-1 talks -- referred to in Geneva as the E3-plus-3, for the three EU and three non-EU countries.
Speaking in English allowed for a free-flowing debate, uninterrupted by lengthy translations, The Washington Post said.
Zarif, using PowerPoint slides, laid out what Iranian officials described as a "road map" that called for resolving the nuclear dispute over several stages within a year.
U.S. Secretary of State John Kerry is expected to discuss the negotiations with his Saudi counterpart sometime soon and with Israeli Prime Minister Binyamin Netanyahu when they meet in Rome next week.
Israel responded with cynicism to the latest talks.
"Iran will be judged by its actions and not its PowerPoint presentations," said a statement Israeli newspaper Haaretz attributed to senior officials in Jerusalem.
"Until we see practical steps that prove Iran is decommissioning its military nuclear project, the international community must continue with the sanctions," the statement said.
"The pressure of sanctions has brought Iran to this point and we must ensure that they are not lifted until such time as Tehran ends its pursuit of military nuclear capability," it said.