Washington: The US Congress and President Barack Obama are on a fast track toward confrontation over sanctions on Iran.

A bipartisan group of senators is pushing a new round of penalties despite the president’s warning that they would scuttle delicate talks under way to prevent Tehran from being able to develop a nuclear weapon.

The Senate Foreign Relations Committee’s hearing on Wednesday on Iranian sanctions is the opening round of the new Republican-led Congress’ first foreign policy fight with the White House. Obama came out swinging last Friday, telling Congress he would veto any Iran sanctions bill that lands on his desk. “Hold your fire,” Obama told Congress while standing at the White House alongside British Prime Minister David Cameron, who took the unusual step of calling US senators to lobby against a sanctions bill.

Time is running out to reach a deal with Iran, which claims its nuclear programme is peaceful and exists only to produce energy for civilian use.

Talks have been extended until July, with the goal of reaching a framework for a deal by the end of March. Both Obama and Iranian President Hassan Rouhani face stiff opposition to negotiations from conservatives in their respective homelands. Moreover, a Republican-victory in the 2016 presidential election would make renewed talks with Iran unlikely.

Obama said if there is new sanctions legislation, Iran could walk away and say the “United States was operating in bad faith and blew up the deal”. And he said the willingness of America’s international partners to enforce existing sanctions against Iran would wane.

“The sanctions that we have in place now would potentially fray because imposing these sanctions are a hardship on a number of countries around the world,” Obama said. “They would love to be able to buy Iranian oil.”

Republicans worry that the Iranians are just buying time so they can continue enhancing their nuclear programmes. Freshman Republican Sen Tom Cotton has gone so far as to call the negotiations a “dangerous farce”. Republicans and some Democrats argue that having more sanctions lying in wait would push Iran to make more concessions at the negotiating table.

A bill drafted by Republican Sen Mark Kirk of Illinois and Democratic Sen Bob Menendez of New Jersey would not impose any new sanctions during the remaining timeline for negotiations. A draft of the bill says that if there is no deal by July 6, the sanctions that were eased during negotiations would be reinstated. After that, sanctions would be stepped up every month.

On August 3, new sanctions would take effect on Iran’s petroleum industry, followed on September 7 by new restraints on nations that import Iranian oil. On October 5, the US would slap travel and financial sanctions against more Iranian officials. On November 2, new sanctions would be levied on foreign banks that do transactions with Iran’s central bank. And then on December 7, the US would impose more sanctions targeting energy, shipping, shipbuilding, auto, mining and other strategic industrial sectors in Iran.

“All I’m saying — and this is where I have a fundamental disagreement with the president — all I’m saying is let us put in prospective sanctions that don’t get imposed until July, which is well after the period of time that the president has said that there will either be an agreement or not,” said Menendez, who butted heads with Obama during a tense exchange on the issue last week at a Democratic retreat in Baltimore.

If there is no agreement, the bill would trigger immediate sanctions unless the president opts for a 30-day waiver because negotiators are “on the verge of an agreement,” Menendez said on Friday. “I’m giving him until July. If there is no deal in July it would have been well over two years since this began. The Iranians are masters of delay.”

The last Kirk-Menendez sanctions bill, which was never voted on by the full Senate, would have compelled an increase in sanctions unless Iran ended all uranium enrichment activities — something Tehran says is a non-starter. That is no longer a binding condition in the bill, said aides who weren’t authorised to speak publicly on the bill while it was still being worked on and demanded anonymity.

Kirk and Menendez are working hard to muster the 67 votes they would need in the Senate to override Obama’s veto. A vote could occur as early as next month.

The Senate Foreign Relations Committee also is working on legislation that would give Congress a right to vote up or down on any deal the administration reaches with Tehran.

“The Iranian parliament has to weigh in on any deal they do, so you would think that the United State Congress would want to weigh in on one of the biggest issues that affects our nation’s security,” said committee chairman Bob Corker, a Republican.

Sen Lindsey Graham of South Carolina, a leading Republican critic of Obama’s foreign policy, said on Sunday that he would be willing to withdraw his support for stiffening sanctions if there is no deal — if the president would submit any agreement with Tehran to Congress for lawmakers to approve or reject.