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 whohad 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.
Among the anticipated key demands by Congress will be that Iran "comes clean" about the weapons programme it continues to officially deny; accepts an intrusive and stringent "additional protocol" inspections regime and dismantles a significant portion of its 19,000 centrifuges.
Obama has had to move quickly to placate sceptical US friends: Israel and the Gulf monarchies. Obama called Israeli PM Benjamin Netanyahu in a bid to reassure him that the accord was temporary and the sanctions relief limited.
Experts believe the agreed controls will stop Iran's nuclear programme in its tracks.
Mark Fitzpatrick, a non-proliferation expert at the International Institute for Strategic Studies, said: "It's better than I thought it would be. I didn't realise that the verification would be this extensive. It caps every aspect of their programme."
Fitzpatrick added: "They're extending the time that Iran would need to break out to build a nuclear weapon: they are at least doubling it, I would say. And if they hadn't done this, the time needed would have halved. Instead of the Iranians halving the breakout time, it will double."
Analyst Anthony Cordesman of the Centre for Strategic and International Studies said: "As first steps go ... the agreement ... offers what is almost certainly the best possible agreement the US and its allies could negotiate, it offers Iran a new path to progress and development, and it offers the region new hope that it can avoid new conflicts and the risk of a massive arms race."
