ALMATY, Kazakhstan — World powers and Iran remain far apart after two days of intensive talks on Tehran's nuclear program, the European Union's foreign policy chief said Saturday, prolonging a stand-off that risks spiraling into a new Middle East war.

The failure to reach a breakthrough deal aimed at easing growing international concern over Iran's contested nuclear activity marked a further setback for diplomatic efforts to resolve the decade-old dispute peacefully.

Underlining the lack of substantial progress during the meeting, no new negotiations between the two sides appeared to have been scheduled.

"Over two days of talks, we had long and intensive discussions on the issues addressed in our confidence-building proposal," EU foreign policy chief Catherine Ashton said.

"It became clear that our positions remain far apart," Ashton, who represents the six powers - the United States, Russia, China, France, Britain, and Germany — in dealings with Iran, told reporters at a news conference.

Russia's negotiator sounded more upbeat, saying the talks were "definitely a step forward" although no compromise had been reached, Interfax news agency reported without further details.

Iran's critics accuse it of covertly seeking the means to produce nuclear bombs and say Tehran has used diplomacy as a stalling tactic. Further inconclusive talks will not reassure Israel, which threatens air strikes, if necessary, to stop its arch-enemy from developing a nuclear bomb.

The Jewish state is widely believed to have the Middle East's only nuclear arsenal. Iran says its nuclear energy program is entirely peaceful but United Nations inspectors suspect it has worked illicitly on designing a nuclear weapon.

With all sides aware that a breakdown in diplomacy could shunt the protracted stalemate a step closer to war, no one in Almaty was talking about abandoning diplomatic efforts.

Ashton said for the first time there had been a "real back and forth between us when were able to discuss details, to pose questions, and to get answers directly.  . . . To that extent, that has been a very important element."

But, she added: "What matters in the end is substance. We know what we want to achieve and the challenge is to get real engagement so we can move forward with this and that's the ambition."

With a presidential election due in Iran in June, the chances for a breakthrough in Almaty became slim when Iran declined to accept or reject an offer of modest relief from economic sanctions in exchange for curbing its most sensitive nuclear activity.

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

The talks were held against a backdrop of flaring tension between big powers and North Korea, which like Iran is defying international demands to curb its nuclear program. But unlike North Korea, which has carried out three nuclear tests since 2006, Iran says its nuclear energy activity is entirely peaceful.