Facing the Senate Foreign Relations Committee, US Secretary of State John Kerry launched a ferocious defense of the deal struck between the US, Britain, China, France, Germany, Russia, EU and Iran in July after two years of negotiations.

Testifying before the Congressional committee, Kerry said that the US could not simply "bomb away" Tehran's atomic knowledge.

"The fact that Iran now has extensive experience with nuclear fuel cycle," Kerry told the committee. "We can't bomb that knowledge away. Nor can we sanction that knowledge away."

Republicans strike back

However, Kerry's defense was ridiculed by Republican lawmakers, with Senator Bob Corker - the committee's Republican chairman -telling the secretary of state, "I believe that you've been fleeced."

Corker later clarified he had not intended to offend Kerry, staying that "we've been fleeced."

Meanwhile, presidential contender and Republican Senator Marco Rubio said that US President Barack Obama was rewarding Iran for "its atrocious human rights record," adding that the deal might not survive after the president's term.

"This is a deal whose survival is not guaranteed beyond the current term of the president," Rubio said.

'Best chance we have'

Kerry responded to Republican criticism by stating that a rejection of the deal by Congress would result in a "green light for Iran."

If Congress strikes down the deal, "the result will be the United States of America walking away from every one of the restrictions we have achieved and a great big green light for Iran to double the pace of its uranium enrichment," Kerry said.

"We will have squandered the best chance we have to solve this problem through peaceful means," the secretary of state said.

Treasury Secretary Jack Lew and Energy Secretary Ernest Moniz - who testified in front of the senate committee - also defended the deal.

Viable?

Congressional lawmakers have until September 17 to decide on the deal, although Obama could veto, forcing the Republican majority Senate and House of Representatives to obtain two-thirds supermajorities to overcome the veto.

The deal curbs Iran's nuclear program - which the international community believe the Islamic republic was using to develop a weapon - in exchange for the easing of sanctions. The UN Security Council approved the deal on Monday.

ls/rc (AP, Reuters, dpa)