Iran and world powers agreed on Wednesday to hold new talks in March and April over the Islamic republic’s disputed nuclear drive after negotiations concluded with Tehran hailing a "more realistic" approach to the decade-old dispute.
There was no sign of a major breakthrough over Iran's nuclear ambitions in the Kazakh city of Almaty but the agreement on new meetings suggested there was still potential for progress.
The talks saw the five UN Security Council members and Germany offer Iran a softening of non-oil or financial sector-related sanctions in exchange for concessions from Tehran over its sensitive uranium enrichment operations.
A senior US official said Iran "appeared to listen carefully to the offer" and its chief negotiator Saeed Jalili issued rare praise for the world powers' "positive" and "realistic" attitude.
"Some of the points raised in their (the world powers') response were more realistic, compared to what they said in the past, Jalili told reporters after the talks.
"We consider these talks as a positive step which could be completed by taking a positive and constructive approach and taking reciprocal steps," he said.
But he added: "We still have a long distance to cover to reach the optimal point."
Uranium enrichment is the most sensitive part of the nuclear cycle as the process can be used to make both nuclear fuel and the explosive core of a nuclear bomb that the powers fear Iran wants to develop.
Officials said the sides would next meet at the level of senior civil servants on March 17-18 in Istanbul.
Talks involving Jalili and the six world powers represented by EU foreign policy chief Catherine Ashton would then take place in Almaty on April 5-6.
-- 'We need to see confidence' --
Ashton gave a hugely cautious assessment of the talks in which she refused to be drawn into a judgement of their success.
"I hope that the Iranian side are looking positively on the proposals we put forward," Ashton told reporters. "The proposals we put forward are designed to build in confidence and enable us to move forward.
"We approach this with the absolutely united view that we need to see international confidence in this (Iranian nuclear) programme."
The US official added to that cautious tone by refusing to pass judgement over the talks' success or failure.
"I would say it was a useful meeting," said the senior official. "I wouldn't say it was positive or negative."
World powers want Iran to halt enriching uranium to 20 percent -- a level seen as the red line for starting to work on making the bomb.
"The six are presenting Iran with an offer of easing the sanctions regime... if the Iranian side agrees to steps towards stopping enrichment to 20 percent" as well as limiting the operations of its Fordo enrichment plant, Russian Deputy Foreign Minister Sergei Ryabkov said.
"This is very important – a lightening of sanctions under a condition," he was quoted as saying by ITAR-TASS.
The offer reportedly involves easing sanctions on Iran's gold and precious metals trade while simultaneously lifting some very small banking operations.
In return it demands a tougher weapons inspection regime and the interruption of enrichment operations at the feared Fordo bunker facility where 20-percent enrichment goes on.
Iran however has always countered that its rights to enrich uranium must be respected before negotiations can proceed any further.
The US official said that right is explicitly ruled out by current UN Security Council sanctions punishing Iran for failing to cooperate with nuclear inspectors.
Iran has also stipulated that it would only consider giving up enrichment to 20 percent if all forms of sanctions against it were lifted -- a condition unpalatable to Washington.
US Secretary of State John Kerry countered on a visit to Berlin on Tuesday that he hoped "Iran itself will make its choice to move down the path of a diplomatic solution".
Israel -- the Middle East's sole if undeclared nuclear weapons power -- has never ruled out attacking Iran's nuclear sites and the diplomacy is essentially aimed at avoiding such an outcome which would send shock waves across the region.