Republican senators try to undermine nuclear talks with letter to Iranian leaders
Senate Majority Leader Mitch McConnell of Kentucky speaking at CPAC 2011 (Gage Skidmore/Flickr)

Republican US senators warned Iran Monday that an international deal curbing its nuclear program may collapse because President Barack Obama has no right to negotiate a binding accord without congressional approval.

In an open letter to the Islamic republic, 47 Republicans, including Senate leaders and several potential 2016 presidential candidates, reminded Iranian leaders that Obama is in office only until January 2017, and a successor could scrap the agreement if Congress has not approved it.

"It has come to our attention while observing your nuclear negotiations with our government that you may not fully understand our constitutional system," the letter began.

"We will consider any agreement regarding your nuclear-weapons program that is not approved by the Congress as nothing more than an executive agreement between President Obama and Ayatollah Khamenei," lawmakers wrote, referring to Iran's supreme leader.

"The next president could revoke such an executive agreement with the stroke of a pen and future Congresses could modify the terms of the agreement at any time."

The letter appeared to be another bid to influence or even derail the talks underway between Tehran and the P5+1 group of world powers to rein in Iran's contested nuclear program.

But it was also seen as pressuring the White House to allow Congress some say in the process.

Many Republicans -- and several Democrats -- fear such a deal would loosen economic sanctions on Tehran while leaving it free to secretly attempt to develop nuclear weapons technology.

Iran insists it is developing nuclear power for civilian purposes.

A bipartisan group of lawmakers recently introduced legislation requiring Obama to submit any pending deal with Iran for congressional approval.

But Senate Majority Leader Mitch McConnell, who signed Friday's letter, agreed to delay consideration of the bill, amid complaints from Democrats.

The letter marked a rare foray by Congress into US foreign policymaking, as negotiating with foreign governments is a responsibility typically handled by the executive branch and not lawmakers.

But following heightened unease over the nuclear negotiations, the Republicans invited Israeli leader Benjamin Netanyahu to speak to Congress last week about the Iranian threat.

Obama administration officials called the invitation a breach in diplomatic protocol, and Democrats said the speech was "condescending."

Netanyahu charged that a deal with Iran would pave the way for an Iranian nuclear weapon.

- 'Unacceptable' deal -

This weekend, Obama said the US would walk away from the nuclear talks if a verifiable deal with Iran could not be reached.

Secretary of State John Kerry went to Paris to smooth over differences with France, which has pressed for greater guarantees that any deal would stop Iran from building a nuclear arsenal.

Negotiations with Iran have gone on for more than a year and are nearing a March 31 deadline for a political deal. A final agreement is meant to be concluded by the end of June.

Under discussion are guarantees to stop Iran from acquiring a nuclear bomb in return for lifting of Western sanctions against the country.

But the initiator of the letter, freshman Senator Tom Cotton, said that while the final terms have yet to be hammered out, details that have emerged already make the deal unpalatable.

"We know so far that Susan Rice, the president's national security advisor, has already conceded that Iran will have a robust uranium enrichment capability," Cotton told Fox News.

"The president has said this deal will have a sunset, perhaps as little as 10 years. Those two terms alone make this deal unacceptable -- dangerous to the United States and dangerous to the world."

The negotiations have included US-Iran bilateral talks as well as discussions among the P5+1 -- Britain, China, France, Germany, Russia and the United States.