But State Department spokesman Sean McCormack could not give a date for the meeting of the envoys of the United States, Britain, China, France, Russia -- the UN Security Council's five veto-wielding permanent members -- and Germany.

"I can only narrow it down to mid-April. We're going to wait, we're going to let our hosts announce the meeting," McCormack said without saying who will host the talks involving Daniel Fried, the US acting undersecretary of state for political affairs.

The UN Security Council last month tightened sanctions on Iran for failing to heed repeated ultimatums to suspend uranium enrichment.

Asked whether the meeting would discuss increasing incentives offered nearly two years ago, McCormack replied: "We'll have more to say about it after the announcement of the meeting."

When pressed on the issue, he said: "They're going to talk about the disincentive path, they're going to talk about the incentive path, and the balance between those two."

Iran said on Saturday it would not make any concession in exchange for incentives offered by the West to halt sensitive atomic activities.

The six members have pledged to expand a 2006 offer of economic incentives to Iran in return for a freeze on uranium enrichment.

But Iran last month ruled out further talks with the six saying that concerns about its nuclear program should be dealt with exclusively by the UN nuclear watchdog, the International Atomic Energy Agency.

The United States and its European allies have led efforts to pressure Iran into freezing its disputed uranium enrichment work, a process that can be used both to make nuclear fuel and the core of an atomic bomb.

Tehran insists its program is peaceful.

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