The United States said Thursday it still expects talks between the P5+1 and Iran on the Islamic Republic's disputed nuclear program to go ahead next week.
Secretary of State Hillary Clinton had said the talks would open in Istanbul on April 13, but Iran later said that Turkey was not an acceptable host after the NATO member cut oil imports from Tehran in response to US pressure.
State Department spokesperson Mark Toner said: "We're still expecting this to take place next week, but there's certainly some degree of urgency in finalizing details.
"It was our expectation that this was going to be in Istanbul, but it's not for us to say one place over another.
"It is however important that we start to nail this down."
Toner said EU foreign policy chief Catherine Ashton was working with Iran to determine the details of the talks.
Iran last held talks with the six powers – Britain, China, France, Germany, Russia and the United States – in January 2011 with no results.
President Barack Obama's administration has been eager to resume diplomacy to avoid a military confrontation, amid speculation that Israel would decide to strike Iran if it determines that Tehran is going ahead with a nuclear bomb.
Nonetheless, Clinton said Wednesday that "the time for diplomacy is not infinite and all options remain on the table to prevent Iran from acquiring a nuclear weapon."
Her comments came as Iran expressed mounting concern over the deployment of a US missile shield in the region, which officials in Moscow and Tehran fear is intended to blunt an Iranian counter-strike should Washington or Jerusalem launch a raid on its nuclear facilities.
Iran says its sensitive uranium work is for peaceful purposes. However, Washington, its Western and Gulf Arab allies, and Israel charge Iran is seeking nuclear weapons.
Two recent reports by the International Atomic Energy Association have buttressed Washington’s view, as well as charging Iran with systemically stymieing inspections of its nuclear facilities under the Nuclear Non-Proliferation Treaty.