The United States says a big-power meeting in Berlin Thursday on possible sanctions against Iran over its nuclear program was productive. But State Department officials caution that the discussion is still at a preliminary stage and may continue for weeks.

The meeting of the five permanent Security Council member countries and Germany convened amid apparent differences, with Russia and China making clear in advance their reluctance to seek sanctions against Iran.

But a statement issued here described the meeting of the P Five-Plus One grouping as positive, with the U.S. delegate, Undersecretary of State Nicolas Burns saying in Berlin that a lot of progress had been made to move the process toward a sanctions resolution.

The meeting was convened after Iran failed to meet an August 31 deadline set by the Security Council for suspending uranium enrichment and other sensitive activities, and returning to negotiations over its nuclear program.

Last June, the P Five-Plus One offered Iran a set of economic and political incentives to suspend enrichment, while also holding out the threat of sanctions in the U.N. if it did not accept the so-called carrots and sticks offer.

The U.S. statement on the Berlin talks said the six political directors expressed regret that Iran had not accepted the conditions of the international community, and that they began discussions of the measures that could be taken in the Security Council in response to Iran's failure to comply.

No details of the talks were provided, but State Department Spokesman Sean McCormack said the six political directors would have a further discussion of the issues by phone on Monday.

Earlier at a news briefing, McCormack stressed that no agreements had been expected in Berlin, and that debate on the sanctions issue would likely go on for a number of weeks.

"I want to temper expectations here, because this is intended as a working meeting," said Sean McCormack. "This is not intended as a meeting to come out with a deal or final text. It was an initial round of formal discussions. They had a variety of informal discussions in the run-up to this, in capitals as well as the U.N. So again, set your expectations for several weeks of these kinds of activities."

Iran responded to the incentives offer August 22, saying that while it was ready for serious talks on its nuclear program, it would not halt enrichment as a precondition.

Iran insists its nuclear program is entirely peaceful while the United States and European allies believe it has covert weapons component.

U.S. officials have spoken of a progressive set of sanctions actions, beginning with relatively mild penalties - travel restrictions and asset freezes targeted on the Tehran leadership.

They say the United States and major allies have already begun discussions of additional, economic, sanctions which if necessary might be imposed by like-minded nations outside the U.N. framework.

Russia and China, both major trading partners of Iran have warned that sanctions might be counter-productive, though U.S. officials say all five veto-wielding Security Council members have endorsed the carrots-and-sticks approach, at least in principle.

The Iran nuclear issue is expected to be a major topic when world leaders convene in New York later this month for the U.N. General Assembly.

Both President Bush and Iranian President Mahmoud Ahmadinejad are expected to deliver policy speeches to the assembly, though there are no plans for any high-level U.S.-Iranian contact.