Six world powers met with Iran for a second day yesterday with scant hope of a breakthrough deal to ease concern that Tehran may be trying to develop nuclear weapons capability, a dispute that could escalate into a new Middle East war.

Negotiators failed to narrow their differences when the two-day meeting began on Friday in Kazakhstan's commercial hub, Almaty. It follows February talks in the same city.

The final day of negotiations was unlikely to achieve more than a willingness to keep talking. On Friday, Iran responded to an offer of limited relief from sanctions with a proposal of its own that puzzled Western diplomats and which Russia said raised more questions than answers.

Iran's critics accuse it of covertly seeking to make nuclear bombs, and say Tehran in the past has used diplomacy as a stalling tactic.

Further inconclusive talks will not reassure Israel, which says if necessary it could launch air strikes to stop its arch-enemy from getting the bomb. The Jewish state is widely believed to have the Middle East's only nuclear arsenal.

With all sides aware a breakdown in diplomacy could move the stand-off a step closer to war, no one in Almaty was talking about abandoning talks. But an actual deal seemed as far away as ever.

"We had a substantive exchange. But there is still a wide gulf between the parties. We are considering how we move on from here," said one Western diplomat after Friday's discussions.

Yesterday, European Union foreign policy chief Catherine Ashton – the lead negotiator of the six world powers – held a bilateral meeting with her Iranian counterpart.

Iranian state television said the country also conducted "fruitful" bilateral meetings with the Chinese and Russian delegations before the wider negotiations resumed at around noon, but gave no details.

Beijing and Moscow – which have commercial ties with Tehran – have backed UN Security Council sanctions resolutions imposed on the Islamic state since 2006 but have criticised separate, harsher Western actions against the big oil producer.

With a presidential election due in Iran in June, scope for a breakthrough was slim even before the first day of talks, when Iran declined to accept or reject an offer of modest sanctions relief in exchange for curbing its most sensitive nuclear work.

Iranian deputy negotiator Ali Bagheri said Iran had given a "detailed response to all the questions".

Russian deputy foreign minister Sergei Ryabkov said: "Iran has given an answer to the proposals of the six powers. It is the kind of answer that creates more questions ... But this shows the negotiations are serious."

Without substantial progress in coming months, Western governments are likely to increase economic sanctions on Iran.

"It seems that instead of narrowing, the gap between the sides [has] actually widened," said Ali Vaez, an Iran expert with the International Crisis Group.

The talks were held against a backdrop of soaring tension between big powers and North Korea, which like Iran is defying international demands to curb its nuclear programme.

But unlike North Korea, which has carried out three nuclear tests since 2006, Iran says its nuclear energy activity is entirely peaceful.