TEHRAN (Reuters) - Iran said on Wednesday it viewed pending nuclear talks with six world powers as an "opportunity and a test", and the United States said "an extraordinarily difficult process" was starting with more meetings likely.
Washington has said big powers will pursue harsher sanctions on Iran over its nuclear programme if the new dialogue fails.
"This, from the point of view of the United States, cannot be an open-ended process, or talks just for the sake of talks, especially in light of the revelations about Qom," said a senior U.S. official, who declined to be identified.
He was referring to a uranium enrichment site near Qom in Iran, which Tehran revealed to the U.N. nuclear watchdog last week after, according to Western diplomats, learning that the site had been detected by Western intelligence services.
As Iran's chief nuclear negotiator left for Switzerland expressing goodwill, the head of the U.N. nuclear watchdog said Tehran had broken a transparency law by failing to disclose much earlier its second enrichment site.
Iran reported the site to Mohamed ElBaradei's International Atomic Energy Agency (IAEA) on Sept. 21, 3-1/2 years after Western powers said construction of the plant began.
"Iran was supposed to inform us on the day it was decided to construct the facility. They have not done that," ElBaradei said in an interview with CNN-India during a visit to New Delhi, in remarks relayed by the IAEA's Vienna headquarters.
With Iran ruling out any discussion in Geneva about its own atomic programme, which the West suspects is aimed at making bombs, there was little sign that Thursday's session would lead to any breakthrough in the long-running dispute.
Iran has offered wide-ranging security talks while making clear its nuclear "rights" will be off-limits. It says its nuclear technology is to generate electricity, not make bombs.
The United States and its Western allies have made clear they will focus on Iran's nuclear activities at the first such meeting since U.S. President Barack Obama took office.
While Iran and the six powers -- the United States, China, Russia, Britain, France and Germany -- prepared for talks, U.S. and British officials seemed to differ over Iran's capabilities.
A British security source said London suspected Iran had been seeking nuclear weapons for the past few years, in contrast to a U.S. view that Tehran halted work on design and weaponisation in 2003. "We didn't share the U.S. assessment and still do not," the source said.
ElBaradei said he had no evidence to back up the British assessment.
U.S. officials are focusing for now on diplomatic efforts, but the White House is considering sanctions targeting Iran's dependence on gasoline imports and insurance firms that underwrite the trade.
Obama warned Iran last week to come clean about its nuclear work or face "sanctions that bite".
President Mahmoud Ahmadinejad made clear Tehran was looking for a changed approach from the West, while showing no sign of any Iranian readiness to compromise in the nuclear dispute.
He said the Geneva talks represented an "exceptional opportunity for (Western countries) to change their situation in the world and correct their way of dealing with nations".
"These talks could be a test to verify whether some governments are determined to follow up the slogan of change," he said according to IRNA news agency, referring to Obama.
Ahmadinejad proposed an organised structure for the discussions, with three committees dealing with different issues, and an "assembly" of heads of states of the countries involved as the top decision-making body, Fars News Agency said.
"We are entering the talks with goodwill," chief nuclear negotiator Saeed Jalili said just before flying to Geneva.
"Both sides need to negotiate in good faith and stop trying to hold a dialogue in the shadow of threats," he said in a separate interview with the German magazine Der Spiegel.
He added: "We don't need an (atom) bomb. It would be neither legitimate nor bring us additional security. We are in favour of global disarmament. But we will continue to enrich uranium."
Jalili was dismissive and defiant about the possibility of harsher sanctions. "We've lived with sanctions for 30 years and they can't bring a great nation to its knees. They do not frighten us. Quite the opposite -- we welcome new sanctions."
Washington has suggested wider sanctions hitting banking and the oil and gas industry if Iran, the world's No. 5 crude exporter, fails to allay Western fears it seeks nuclear weapons.
Ahmadinejad said Iran had prepared itself for all possibilities: "The Iranian nation has learnt to stand on its own feet during the past 30 years."
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