The United States Congress will move to create a "Sword of Damocles" hanging over the heads of the Iranians and the White House to ensure the interim nuclear deal reached in Geneva holds, a senior Senate source promised.
Talks are already under way between leading Republican and Democrat senators who had grown wary of the deal as it was brokered over the past few weeks.
An aide who has direct knowledge of the Senate negotiations said senators would hold a "Sword of Damocles" over the deal, adding: "The only way this six-month 'freeze' period is reassuring is if the deal holds. The President and John Kerry say if Tehran cheats, they will re-impose sanctions, but we have no confidence they will do that. We want it enshrined in law."
Large parts of Congress remain sceptical of Iran's good intentions and the willingness of President Barack Obama and Kerry, the US Secretary of State, to be tough with Tehran in follow-up talks.
The idea behind the new legislation would be to deny Tehran any opportunity to spin out the deal in an attempt to garner sanctions relief without actually moving to decommissioning elements of its suspected nuclear weapons programme.