Foreign ministers from six key powers meet Tuesday to coordinate their positions on Iran's nuclear program, with France saying it expects quick agreement on a new draft U.N. resolution to increase pressure on Tehran. But a U.S. official said differences over the issue remain.

The meeting at the Foreign Ministry in Berlin brings together the foreign ministers of the five permanent U.N. Security Council members -- the U.S., Britain, France, Russia and China -- plus Germany, as well as European Union foreign policy chief Javier Solana.

It comes in the wake of last month's U.S. intelligence assessment that Tehran stopped active work on a nuclear weapons program in 2003. That appeared to stiffen resistance from veto-wielding Russia and China to a quick and harsh third round of sanctions over Iran's defiance of international demands that it suspend uranium enrichment.

However, Western nations have stressed the need to keep up the pressure; and a senior French diplomat said before the meeting that an agreement on a draft resolution was very close.

The diplomat, who briefed reporters in Paris on condition that he not be identified by name, said an agreement should be finalized by the ministers at Tuesday's meeting.

He would not give details on the resolution, but said it would be "very balanced, very firm" and likely be presented to the Security Council for debate by the end of the month. "We are really very close," he said.

The German Foreign Ministry declined to comment Monday on the French assessment.

However, others were more cautious about what the talks could produce.

A senior US official said Monday that the six nations had made some progress in negotiating a new resolution in a flurry of weekend conference calls but that "substantial" differences still existed.

The official, speaking on condition of anonymity due to the sensitivity of the ongoing talks, told reporters it was not clear if agreement could be reached at Tuesday's meeting.

The official said senior negotiators from all six nations would have another conference call ahead of the ministerial meeting in Berlin.

Iran insists it never had a nuclear weapons program and that its work is for peaceful purposes such as energy production.

The host of Tuesday's meeting, German Foreign Minister Frank-Walter Steinmeier, has said it will focus on making sure that international unity over the need for Iran to heed Security Council demands "will continue to be expressed in the future."

"The problem is not solved," he said last week. Urging Iran to "resurrect international confidence" in its nuclear intentions, Steinmeier said the world "cannot and will not allow that technology for nuclear weapons be developed in this region."

That was a reference primarily to uranium enrichment, which Iran says it wants to develop to be able to generate nuclear power, but which also can create the fissile core of nuclear warheads.

Francois Gere, an Iran specialist and head of the French Institute of Strategic Analysis, said he was "a little skeptical" that a third resolution would gain Russian and Chinese approval so quickly.

He suggested the French announcement could be a pressure tactic ahead of Tuesday's talks. France pushed vocally late last year for tough new sanctions and "does not want to give the impression of pulling back now," Gere said.

On Monday, Iranian Foreign Ministry spokesman Mohammad Ali Hosseini said that Washington and the other Western powers would not succeed in efforts to halt Iran's nuclear program.

"They are looking for excuses," he said. "This will not bear fruit and will mostly work against them, and we will continue our constructive cooperation with the (International Atomic Energy) agency," the U.N. nuclear watchdog.

Earlier in January, IAEA director Mohammed Elbaradei visited Tehran, and Iran agreed to answer all remaining questions over its nuclear activities in the next few weeks.

Iran's nuclear negotiator, Saeed Jalili, will be in Brussels on Wednesday to talk at the European Parliament, but the EU's Solana said that, as yet, they have no plans to meet.

"I have to see if that is a real use of my time, for me to meet him," Solana told reporters on Monday. "We may find some time to meet."