European Union foreign policy chief Catherine Ashton and Iran’s top nuclear negotiator Saeed Jalili have postponed setting a date for a fresh round of talks on Iran’s controversial nuclear program until the end of August.

"I proposed, and Dr. Jalili agreed, that we talk again after further reflection at the end of the month," Ashton said in a statement on Thursday after a telephone conversation with Jalili.

"I impressed the need for Iran now to address the issues we have raised in order to build confidence," Ashton said.

The previous three meetings this year between Tehran and the so-called P5+1 group - the five permanent members of the UN Security Council and Germany - did not produce any results.

After the latest round of face-to-face talks on June 18-19 in Moscow, Ashton and Jalili acknowledged a “large gap” between the two sides over confidence building measures on the nuclear issue and announced the indefinite pause in negotiations.

Western nations suspect Iran, which is under four sets of UN Security Council sanctions, of pursuing a secret nuclear weapons program but Tehran insists it needs nuclear power solely for civilian purposes.

The P5+1 mediators have been trying to persuade Iran to curb its nuclear activities since 2003 by offering a number of attractive financial and economic incentives to the Islamic Republic.

In addition, they have offered Iran a chance to exchange its stockpiled 20%-enriched uranium for nuclear fuel for the Tehran Research Reactor, but Tehran claims this proposal is pointless since the country can already produce such fuel on its own.

Frustrated by the lack of progress in negotiations, the 27-nation European Union introduced an oil embargo on the Islamic Republic, which came into force on July 1 this year. The EU accounts for 18% of Iranian oil exports.

Both sides are under pressure to forestall the escalation of the nuclear crisis as Israel has hinted at military action against Tehran unless Iran's nuclear development is completely stopped.

Israeli Prime Minister Benjamin Netanyahu told the visiting U.S. Defense Secretary Leon Panetta this week that by dragging the negotiation process Iran is trying to buy time to continue with its nuclear research.