For weeks, if not months, the US administration has found itself in an awkward position on Iran – caught between a domestic debate that has pushed Washington to impose new sanctions and delicate international negotiations that could be upset by such a course.

Political and public concern about Tehran has mounted in the US in the wake of President Mahmoud Ahmadi-Nejad’s visit to New York last month and a series of claims by the US military that Iran was supplying weapons to insurgent groups in Iraq and Afghanistan.