State Department spokeswoman Jen Psaki said on Wednesday that the Obama administration has not yet decided whether to urge the US Congress to refrain from imposing additional sanctions on Iran - a request it made ahead of this week's talks on the issue.

Six major powers and Iran wrapped up talks in Geneva about the Iranian nuclear program on Wednesday and diplomats said Iran appears ready to increase cooperation in return for relief from harsh economic sanctions.

In a clear sign of hope, however, European Union foreign policy chief Catherine Ashton said it was agreed to hold the next round of negotiations in three weeks in Geneva, and Iran's chief negotiator praised this week's meetings as "fruitful."

"There remain differences (about) what sanctions relief might be appropriate," Psaki said at her daily briefing in Washington. "Anything we would do would be proportionate" to Iran's steps on curbing its nuclear program, she added.

As with a US official who briefed reporters in Geneva, Psaki struck a somewhat upbeat tone.

"We have never had detailed technical discussions at this level before," she said, adding that the Iranian delegation had laid out "what they might do as a first step, and also, what should be in a final step." She provided no details on these steps.

Psaki said technical experts from Iran and the major powers will meet before the Nov. 7-8 talks but did not say when or where.

NTJ/NJF