Iran and world powers agreed on Wednesday to hold new talks in March and April over the Islamic republic’s disputed nuclear drive, with Tehran hailing a "more realistic" approach by their counterparts at two days of talks in Kazakhstan.

There was no sign of a breakthrough in the decade-long deadlock 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 six world powers -- Britain, China, France, Germany, Russia and the United States –- offer Iran a softening of sanctions in exchange for concessions from Tehran over its sensitive uranium enrichment operations.

"Some of the points raised in their (the world powers') response were more realistic, compared to what they said in the past," Iran’s top nuclear negotiator Saeed Jalili told reporters after the talks.

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, which world powers fear Iran wants to develop.

But in contrast to the acrimony that has followed some past encounters, Jalili said he viewed the overall tenor of the meeting as "positive."

"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.

The two sides would next meet at the level of senior civil servants on March 17-18 in Istanbul, officials said.

The next high-level talks involving Jalili and the six world powers represented by EU foreign policy chief Catherine Ashton would also be in Almaty, from April 5-6, both sides confirmed.

 'We need to see confidence'

Ashton gave a hugely cautious assessment of the talks, refusing to be drawn into a judgement of their success and saying she hoped for a positive response from the Iranians.

"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 world powers want Iran to halt enriching uranium to 20 percent, the level seen as a 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 said, quoted by the ITAR-TASS news agency.

The offer reportedly involves easing sanctions on Iran's gold and precious metals trade while simultaneously lifting some restrictions on the Islamic republic's banking operations.

Iran however has always countered that its rights to enrich uranium must be respected before negotiations can proceed any further.

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.

The Jewish state launched a unilateral attack against the Osirak nuclear reactor in Saddam Hussein's Iraq in 1981 and has spoken of Iran approaching the same "red line" that demanded immediate action.

Iran already has a nuclear power plant in the southern city of Bushehr -- built with Russian help -- but Iran's supreme leader Ayatollah Ali Khamenei has described atomic weapons as a "sin".