US President Barack Obama rebuffed critics of the Iran nuclear agreement Saturday, defending the historic accord amid skepticism from lawmakers reviewing the deal.

In his weekly address, Obama said that without the accord, "we'd risk another war in the most volatile region in the world," underlining the limits now placed on Iran's nuclear program.

"This deal actually pushes Iran further away from a bomb. And there's a permanent prohibition on Iran ever having a nuclear weapon," Obama said.

"We will have unprecedented, 24/7 monitoring of Iran's key nuclear facilities."

He said repercussions would be swift if Iran did not stick to the agreement.

"If Iran violates this deal, the sanctions we imposed that have helped cripple the Iranian economy -– the sanctions that helped make this deal possible –- would snap back into place promptly."

The agreement, signed Tuesday after two years of talks, aims to roll back Tehran's nuclear program in return for lifting sanctions that have stunted Iran's economy.

Under the deal, Iran will cut by about two-thirds the number of centrifuges -- which can make fuel for nuclear power stations but also the core of a nuclear bomb -- from around 19,000 to just over 6,000.

The US Congress has 60 days to review the agreement, and can vote to approve or reject it.

Obama's Republican rivals, who hope to scupper the agreement in a planned Congressional vote, have accused him of appeasement.

Obama said he was not scared of naysayers, and welcomed questions on the deal.

"I welcome all scrutiny. I fear no questions. As Commander-in-Chief, I make no apology for keeping this country safe and secure," he said.

"Does this deal resolve all of the threats Iran poses to its neighbors and the world? No. Does it do more than anyone has done before to make sure Iran does not obtain a nuclear weapon? Yes."

Under legislation passed in May, President Barack Obama is barred from lifting congressional sanctions on Iran during the review period, unless Congress approves the deal during that time.

Should Congress pass a resolution of disapproval, Obama would veto that resolution. Two-thirds of lawmakers would be needed to override a presidential veto.

Obama will address the national convention of the Veterans of Foreign Wars next week, where he will continue his defense of the deal, which he said met the red lines set out by Washington.

"We refused to accept a bad deal. We held out for a deal that met every one of our bottom lines. And we got it."

Meanwhile, Iran's supreme leader Ayatollah Ali Khamenei said Saturday that the nuclear deal "won't change" the country's stance toward the "arrogant" United States government.