Media playback is unsupported on your device Media caption John Kerry warns Congress against rejecting the Iran nuclear deal

US Secretary of State John Kerry has hit back at critics of his nuclear deal with Iran, saying it was "fantasy" to suggest a better accord was possible.

He told the US Senate's Foreign Relations Committee: "We set out to dismantle [Iran's] ability to build a nuclear weapon and we achieved that."

Republican presidential hopeful Marco Rubio told him the deal was "fundamentally flawed".

Congress has until 17 September to approve or reject the deal.

Meanwhile, Iran's president has also been defending last week's agreement, which was the result of nearly two years of intense negotiations with the P5+1 group of world powers - the US, UK, France, China and Russia plus Germany.

Hassan Rouhani, in a speech broadcast live on television, said the deal represented "a new page in history" and was wanted by the Iranian people.

Under the deal, Iran must curb its nuclear activities in exchange for sanctions relief. Tehran has always insisted its nuclear ambitions are peaceful and energy-related.

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Congress has 60 days to review the agreement

During that time, President Obama cannot lift the sanctions Congress has imposed on Iran

Congress can reject the deal, and keep the sanctions in place, but Mr Obama can veto that

It would need a two-thirds majority to overturn the veto, which is unlikely

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Mr Kerry told the committee hearing that the US administration came to the negotiating table with one clear objective - to address the issue of nuclear weapons.

Under the terms of the deal, he said Iran has agreed to:

voluntarily remove 98% of its stockpile of enriched uranium

dismantle two-thirds of installed centrifuges

take out the core of an existing heavy water reactor and fill it with concrete

refrain from producing or acquiring highly-enriched uranium and weapons-grade plutonium for at least 15 years

ratify through parliament "additional access requirements" for nuclear inspectors

Mr Kerry said that if Iran failed to comply with the agreement "we will be able to respond accordingly by reinstituting sanctions all the way up to the most draconian options that we have today".

Turning on his critics, he said any suggestion of a "better deal, some sort of unicorn arrangement involving Iran's complete capitulation" was "fantasy, plain and simple".

"The choice we face is between an agreement that will ensure Iran's nuclear programme is limited, rigorously scrutinised and wholly peaceful - or no deal at all."

Image copyright AFP/Getty Images Image caption The deal with Iran has encountered plenty of opposition, from within Congress to the streets

Image copyright AP Image caption But Mr Kerry also had his supporters at the hearing

But Mr Kerry - who appeared at the committee hearing along with fellow negotiators, the Energy Secretary Ernest Moniz and Treasury Secretary Jack Lew - faced scepticism from some senators.

Bob Corker, the committee's Republican chairman, opened the meeting by telling Mr Kerry he had been "fleeced".

Marco Rubio said the deal was "fundamentally flawed" and would "weaken our national security and make the world a more dangerous place".

Iran would still be able to build long-range ballistic missiles "that know only one purpose and that is for nuclear warfare" and would provide billions "to a regime that... directly threatens the interests of the United States and our allies", Mr Rubio said.

Separately, two Republicans have complained that Congress has not been given access to "side deals" stuck between Iran and the International Atomic Energy Agency, which allegedly relate to the inspection of a key military site as well as past military activity.

White House spokesman Josh Earnest rejected the suggestion they were "some sort of side deal", saying the agreements were critical to the overall deal.

But he did admit that the details of the agreements could not be made public because it involves sensitive nuclear information.