Washington:  The United States called on Iran to show "seriousness" in nuclear talks in Turkey, after Tehran warned it was discouraged by the approach of Western nations.
After a 15-month hiatus, officials from the United States, Russia, China, Britain, France and Germany (known as the P5+1) will meet with Iranian counterparts in Istanbul on Friday.
The Obama administration has said there is still time for diplomacy to end the Iranian nuclear crisis, but warns the window is closing, as speculation continues about the possibility of an Israeli strike on Iran.
US deputy national security advisor Ben Rhodes said on Air Force One that Washington wanted a "positive environment" in the talks with Tehran showing "seriousness" about moving forward with dialogue.
"I think nobody expects to resolve all differences in one meeting but what we want is a positive environment where the Iranian government demonstrates its seriousness and its commitment to pursuing serious negotiations," he said.
Rhodes said that the onus was on the Iranians to demonstrate how they could "build confidence" with the international community by living up to commitments to disclose details of what the West believes is a nuclear weapons programme.