By Fredrik Dahl
VIENNA (Reuters) - Western powers said on Wednesday an Iranian "charm offensive" had failed to dispel mounting fears Iran may be working to develop a nuclear bomb, but Washington's envoy did not rule out engaging with Tehran after it offered fresh talks.
Glyn Davies, U.S. ambassador to the U.N. atomic watchdog, said a letter from Iran's nuclear negotiator to the European Union's foreign policy chief did not contain any new commitments by Tehran to address international concerns about its aims.
"We note Iran's recent claim that it is starting a new era of cooperation," Davies said. "We have heard this claim before, but it has yet to be fulfilled."
But he also said the six major powers involved in efforts to resolve the nuclear dispute were still considering how "best to react" to the latest letter from Tehran, leaving the door open to the prospect of a new diplomatic initiative.
In the letter, Iran's negotiator Saeed Jalili told the EU's Catherine Ashton Tehran was ready to restart talks, but he also stuck to language emphasizing Iran's nuclear "rights" seen in the West as a sign that Tehran is not changing positions that doomed talks in the past.
Ashton has been handling contacts with Iran on behalf of six powers, which include the United States, Britain, France and Germany as well as non-Western states Russia and China. She led talks with Iran on the powers' behalf in December and January, but Western states have since refused Tehran's offers to resume.
Iran has insisted countries recognize its right to enrich uranium, which it says it wants to fuel power plants. The Western states say enriched uranium could be used to make a bomb, and the demand is an unacceptable precondition for talks.
Davies said the powers were still formulating a response to Jalili's latest letter.
"I don't want to get out ahead of the diplomatic discussions ... to decide on next steps -- whether, when and how to engage with the Iranians based on that letter," Davies said on the sidelines of a board meeting of the U.N. atomic watchdog.
Since negotiations between the powers and Iran foundered in January, Russia has advocated a phased plan in which Tehran would address concerns that it may be seeking nuclear weapons, and be rewarded with an easing of sanctions.
Faced with tightening sanctions pressure, Iran has launched an effort in the last few months to demonstrate increased openness and cooperation with the U.N. International Atomic Energy Agency about its nuclear program.
In August, it allowed a senior IAEA inspector access to two nuclear-related sites that the Vienna-based U.N. agency had not had access to for several years, saying this showed Tehran's "100 percent transparency and openness."
Last week, Jalili sent his letter to Ashton, in which he talked about the "necessity of achieving a comprehensive, long-term and negotiated solution for both sides."
But he made clear Iran would not back down on its nuclear "rights," a phrase that Iran has usually used in the past to refer to its insistence it be permitted to enrich uranium.
Iran's envoy to the IAEA, Ali Asghar Soltanieh, said Iran's stated readiness to cooperate with the IAEA marked a "turning point" and created an opportunity that should be seized by all.
"NO SMOKING GUN"
Statements by Britain, Germany, France and the United States at the meeting of the IAEA's 35-nation governing board made clear they were not impressed with Iran's openness push.
"Stonewalling the IAEA, flouting U.N. Security Council obligations and mounting this most recent charm offensive do not reflect a good faith effort to resolve...concerns," Davies said.
Like the United States, Britain, France and Germany voiced particular alarm at Iran's decision to move higher-grade uranium enrichment to an underground bunker -- heightening suspicions.
"The absence of a plausible economic or commercial rationale for so many of the nuclear activities now being carried out in Iran, and the growing body of evidence of a military dimension to these activities, give grounds for grave concern about Iran's intentions," British Ambassador Simon Smith told the board.
Iran denies Western accusations its program is aimed at developing a nuclear weapons capability.
"The most robust inspection in the history of the IAEA has not found any evidence of diversion of nuclear material to military purposes, no smoking gun," Soltanieh said.
The IAEA has added independent pressure on Iran, with its director, Yukiya Amano, saying publicly for the first time this week that he was "increasingly concerned" about possible military aspects of Iran's nuclear program.
Amano also said he planned to present soon the basis for those concerns in more detail to member states, a step that could provide stronger arguments for Western punitive measures.
Vienna-based diplomats say this may be why Iran is now showing more willingness to cooperate with the U.N. body.
(Editing by Peter Graff)