The White House on Monday said Iran needed to take "concrete steps" to assure the United States and the international community that it was not pursuing nuclear weapons, AFP reported.
"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.