President Barack Obama urged the US Congress to give peace with Iran a chance Monday, as lawmakers lined up behind new sanctions despite warnings they could doom an interim nuclear deal.

Obama said that the six-month pact due to go into force on January 20 after being concluded at the weekend, offered a "door of opportunity" for Iran to have better relations with the outside world, after decades of deep antagonism with the United States.

But he said that if Iran fails to live up to the terms of the deal, which freezes aspects of its nuclear program in return for limited sanctions relief, he would support new punitive measures to stop Tehran getting a nuclear weapon.

"My preference is for peace and diplomacy," Obama told reporters in the Oval Office.

"This is one of the reasons why I've sent a message to Congress that now is not the time for us to impose new sanctions. What we want to do is give diplomacy a chance and give peace a chance."

The White House has previously warned that Obama will veto any bill enacted by Congress to impose new sanctions on Iran, fearing it could prompt Tehran to walk away from the negotiating table or undermine its negotiators among regime conservatives back home.

But there are increasing signs that bipartisan support for the bill on Capitol Hill may be nearing the two-thirds majority required to override such a veto.

It is currently unclear if and when the bill will be brought up for a vote in Congress. The president will have a chance to press home his case for a delay in new sanctions when he makes his annual State of the Union address on January 28.

Lawmakers who support the bill say tough sanctions brought Iran to the negotiating table and stiffer measures would increase Obama's leverage in talks between the Islamic Republic and the P5+1 group of world powers.

Obama has insisted that Washington must test Iranian President Hassan Rouhani's willingness to honor a pledge to seek a peaceful nuclear deal, despite opposition from many hawks on Capitol Hill and deep reservations by America's closest Middle Eastern ally, Israel.

His aides say that if new sanctions force the nuclear talks to collapse, Washington could be forced into another war in the Middle East to thwart the Islamic Republic's nuclear ambitions.

Obama stresses that he has not taken the option of using military force off the table, but he has warned that such action may not be decisive and could unleash waves of unintended consequences across the Middle East.

White House spokesman Jay Carney said new sanctions would have the opposite effect to the one intended by key sponsors, Democratic Senate Foreign Relations Committee Chairman Robert Menendez and Republican Senator Mark Kirk.

"It could, if they were to do it, actually weaken the sanctions structure that's in place by undermining faith among our international partners and providing Iran the opportunity to say that we have been negotiating in bad faith," Carney said last week.

In a Washington Post editorial, Menendez described the initiative as a "diplomatic insurance policy" against Iran. He said his bill would impose immediate extra sanctions on Iran if it became necessary but would not come into force while "good faith" negotiations were under way.

"Should Iran breach this agreement or fail to negotiate in good faith, the penalties it would face are severe," he wrote.

New sanctions would further target Iranian petroleum products and the mining, engineering and construction sectors.

A senior US administration official told AFP that the first $550-million (400-million-euro) installment of $4.2 billion in frozen assets would be released under the interim nuclear deal early next month.

"The installment schedule starts on February 1 and the payments are evenly distributed" across 180 days, the official said.

Analysts say unblocking the funds would breathe new life into the economy and provide much-needed relief across Iran.