"We're looking forward to these talks creating a conducive environment for concrete progress," Jay Carney, spokesman for President Barack Obama, told reporters ahead of key meetings this week between Tehran and world powers.

"We are very clear-eyed about what Iran needs to do in order to fulfill its international obligations and be able to reassure the international community that it is not pursuing nuclear weapons.

"We need concrete steps taken by the Iranians to assure that they will forsake their nuclear weapons ambitions," said Carney, as he welcomed talks set to take place in Istanbul later this week.

President Obama, added Carney, has already "made clear that the window is closing on Iran, that they need to treat these talks seriously because there is great concern around the world about Iran's pursuit of nuclear weapons."

Iran last held talks with the so-called P5+1 powers -- permanent UN Security Council members Britain, China, France, Russia and the United States plus Germany -- in January 2011, with no results.

Obama has, however, appeared to accept Tehran's civilian nuclear ambitions, telling Iran that Washington would accept a civilian nuclear program but only if it can prove it is not seeking atomic weapons, according to a recent Washington Post report.

"It is vital to measure Iranian intentions by actions, as opposed to words, and we will do that. But it is also important that these talks are getting up and going again after a long delay," Carney said Monday.

The United States and other Western countries fear Iran is developing a nuclear weapon, but Tehran insists that its atomic program is for exclusively peaceful purposes.

"We have agreed to launch talks in Istanbul on April 14," Michael Mann said on Monday. "We hope that this first round will produce a conducive environment for concrete progress.

"We are of course aiming at a sustained process," Mann added.

Iran last held talks with the so-called P5+1 powers -- permanent UN Security Council members Britain, China, France, Russia and the United States plus Germany -- in January 2011 with no results.

There had been a dispute as to whether the venue for the fresh talks should be Istanbul or Baghdad.

US Secretary of State Hillary Clinton had already announced that the talks between Tehran and the group of six powers would resume April 13-14 in Istanbul.

However Tehran had then objected to the venue, arguing that Turkey's tough line against Damascus in recent months did not make it a neutral host, and suggested Baghdad instead.

Iran did not specifically react to the dispute over the venue Monday but its foreign minister said he hoped all sides would come to the negotiating table without pre-conditions and make the fresh talks succeed.

"We hope the P5+1 will come to the negotiating table with honesty, and we also will make an honest effort so that both sides reach a win-win conclusion," Ali Akbar Salehi told the Iranian parliament's website.

Both sides have sent positive signals ahead of the fresk talks, with Iran hinting it had a new offer to put on the table and reports that Washington could accept a civilian nuclear programme if Tehran could prove it was not seeking the atomic weapon.

Egged on by Israel, its chief ally in the Middle East, Washington had ratcheted up the rhetoric against the Islamic state in recent months, sparking fears of a military flare-up.

Observers hope the fresh round of talks between Iran and the five permanent members of the UN Security Council and Germany will help defuse the risk of further escalation.

Oil prices slid in Asian trade on Monday with New York's main contract, West Texas Intermediate crude for delivery in May, shedding $1.11 to $102.20 per barrel.