The United States and Iran have been conducting secret back-channel discussions on Tehran's nuclear program and frozen relations between the two countries, The Independent reported Monday.

The British newspaper quotes former US under secretary of state Thomas Pickering as saying that a group of former US diplomats and foreign policy experts had been meeting with Iranian academics and policy advisers "in a lot of different places, although not in the US or Iran" for the past five years.

"Some of the Iranians were connected to official institutions inside Iran," Pickering told the paper.

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Last week, the United States warned Iran it risked further isolation and new international sanctions after refusing to comply with UN Security Council resolutions over its disputed nuclear program.

The West fears Iran could use enriched uranium to make a nuclear weapon, and Tehran's refusal to suspend the process has been punished with three sets of UN Security Council sanctions resolutions and US pressure on its banking system.

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