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Negotiators from Iran and six of the world's top powers are sitting down for the first time in more than a year to discuss Tehran's controversial nuclear program.

Turkish officials confirmed Saturday the talks were underway between Iranian diplomats and representatives of the United States, Britain, China, France, Germany and Russia .

Security in Istanbul has been tight for the high stakes meeting, but Western diplomats have been quick to downplay expectations. They say the most that can be hoped for is that this round of negotiations will lead to another round of talks.

U.S. Deputy National Security Adviser Ben Rhodes on called the talks a “good first step” while meeting with reporters on Friday. He also said the burden of proof remains on the Iranians because “they are the ones in violation of their international commitments.”

Tehran has faced Western sanctions over accusations that it is trying to develop a nuclear bomb. Iran says its nuclear program is for peaceful use.

Earlier this week, Iran's chief nuclear negotiator said his country would present unspecified new initiatives at the talks, but warned that efforts by the West to exert pressure on Tehran would “backfire.” Saeed Jalili also said efforts to use what he called the “language of force” against Iran would be “useless.”

Because of continuing gaps in negotiating positions, Brookings Institution senior fellow Michael O'Hanlon says most analysts do not think the talks will succeed.

“I think it's fairly clear that Iran has no particular interest in detente with the outside world. No interest in knowing or acknowledging that it has been squeezed into submission and it does want a nuclear weapon capability at some level.”

But Michael Singh, of the Washington Institute for Near East Policy, says the talks could produce results because Iran is facing huge international pressure.

“I hope that these talks will validate the strategy of trying to use pressure in conjunction with diplomacy to get the Iranians to really shift their course, to change their approach to this nuclear question.”