Iran and six world powers wrapped up talks Thursday still far apart over how to oversee Tehran's atomic program, but with resolve to keep dialogue going as an alternative to possible military action.

Envoys said they will meet again next month in Moscow after negotiations stretched out for extra hours and a sandstorm shut the airport in Iraq's capital. But the two sides agreed on little else during two dramatic days of discussions that underscored the serious challenges of reaching accords between Iran and the West.

"It is clear that we both want to make progress, and that there is some common ground," European Union foreign policy chief Catherine Ashton, who is formally leading the talks, told reporters. "However, significant differences remain. Nonetheless, we do agree on the need for further discussion to expand that common ground."

Saeed Jalili, Iran's top nuclear negotiator, offered a lukewarm assessment of what the negotiations achieved, in light of European and American refusal to lift tough sanctions as Tehran had hoped.