They made clear at a meeting of the UN atomic watchdog that the Iran must address broader concerns about work the West suspects is a veiled quest to develop bombs, and not just seek more talks on a proposed swap of nuclear material.

Iran, which has called for speedy negotiations on the fuel swap idea but has listed conditions for broader talks, says its uranium enrichment work is aimed at civilian power production.

Jochen Homann, from Germany’s Economics and Technology Ministry, said the six powers involved in efforts to defuse the nuclear standoff were willing to hold immediate talks with Iran. “(We) have presented a comprehensive offer of cooperation. Iran should follow up its words with deeds and return to the negotiating table now,” Homann said in a speech to the annual assembly of the International Atomic Energy Agency (IAEA).

His comments were echoed by the French delegate, who said Iran’s behavior had left the powers no choice but to impose a series of tougher sanctions measures on the country since June.

“In acting in this fashion the international community is showing Iran that its choices are very costly indeed, ever more so,” said Bernard Bigot of France’s Atomic Energy Commission. But, he added, “we are convinced that a negotiated solution of the crisis is possible. We continue to appeal to Iran to finally choose to cooperate.”

Their message to Iran is expected to be underlined by US President Barack Obama when he addresses the United Nations General Assembly on Thursday in New York. The White House said he will tell Iran the “door is open” to better relations if it can demonstrate the peaceful intent of its nuclear program.