US Secretary of State John Kerry faced accusations that he had been "fleeced" and "bamboozled" by Tehran as he defended the Iran nuclear deal publicly for the first time on Capitol Hill.
Kerry appeared before the Senator Foreign Relations Committee on Thursday (local time) to defend the hard-fought agreement, which he called a "good deal for the world" that deserves the approval of a sceptical Congress.
"The truth is that the Vienna plan will provide a stronger, more comprehensive, more lasting means of limiting Iran's nuclear program than any alternative that has been spoken of," he said of the deal struck last week in the Austrian capital.
Once in place, it would put Iran under "intense scrutiny forever" and keep the world united in ensuring that its nuclear activities "remain wholly peaceful," he added.
"We believe this is a good deal for the world, a good deal for America, a good deal for our allies and friends in the region - and we think it does deserve your support."
But Kerry, peering wearily over a pair of wire-rim glasses, encountered a tsunami of scepticism from Republicans on the Foreign Relations Committee, which as a Democratic senator he once chaired.
"I believe you've been fleeced," said committee chairman Bob Corker, arguing that the Vienna deal would give Iran "a perfectly aligned pathway" towards becoming a nuclear power in due time.
"With all due respect, you guys have been bamboozled and the American people are going to pay for that," echoed fellow Republican senator James Risch.
"Anybody who believes this is a good deal really joins the ranks of the most naive people on the face of the Earth," Risch said.
Kerry was testifying publicly on Capitol Hill for the first time since the UN Security Council on Monday unanimously endorsed the Iran agreement, paving the way to the lifting of punishing economic sanctions.
The deal was reached after tough negotiations between Iran and the Security Council's five permanent members - Britain, China, France, Russia and the United States - plus Germany.
But it faces stiff resistance notably among Republicans in the Senate and the House of Representatives, which have 60 days to review it.