World powers and Iran were due Wednesday to respond to offers presented by both sides in a final day of talks aimed at breaking a decade of deadlock over Tehran's nuclear drive.

The first day of gruelling negotiations in a swank hotel in Kazakhstan's commercial capital Almaty concluded Tuesday with both sides relieved to have pushed the talks along for another day.

They swapped offers that could ease some sanctions on Iran in exchange for concessions on its disputed nuclear programme -- proposals that had been discussed in various forms at three previous meetings in the past year.

The big power's official spokesman measured his words carefully as he laid out what the world expected Iran to do next to convince nations it was not in hot pursuit of a nuclear bomb.

"We hope very much that the Iranian side comes back (on Wednesday) showing flexibility and a willingness to negotiate," added the spokesman for EU foreign affairs chief Catherine Ashton.

"The ball is very much in their court," Michael Mann stressed.

On the table is an offer for the five permanent UN Security Council members and Germany to ease sanctions on Iran's gold and precious metals trade while simultaneously lifting some restrictions on the Islamic republic's banking operations.

The measures are meant to introduce good will in Tehran while encouraging it to stop enriching uranium to 20 percent -- a level seen as being within striking distance of military capabilities.

The powers also want Iran to shut the Fordo plant where such high-grade material is produced and to ship out the existing stock it does not need for established medical purposes.

Iran counters that its rights to enrich uranium -- entrusted to every nation but stripped from Iran due to its failure to cooperate with nuclear inspectors -- 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.

"We will not accept anything beyond our obligations and will not accept anything less than our rights," Iran's chief nuclear negotiator Saeed Jalili declared before setting off for Kazakhstan.

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" -- comments carrying the implicit threat of air strikes of the type threatened by Israel.

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.

Few expect Wednesday's meeting to conclude with anything beyond promises to hold more discussions at various levels. But proponents of this approach argue that such painstaking negotiations avert much more serious dangers.

"It's clear that no one expects everyone to walk out of here in Almaty with a done deal. This is a negotiating process," Ashton's spokesman Mann said.

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".