Kerry says Congress cannot modify potential Iran nuclear deal

U.S. Secretary of State John Kerry said on Wednesday that Congress could not modify the terms of a potential nuclear agreement between world powers and Iran.

"It's incorrect when it says that Congress could actually modify the terms of an agreement at any time. That's flat wrong," Kerry told lawmakers. "They don't have the right to modify an agreement reached, executive to executive, between leaders of a country."

Kerry told the Senate Foreign Relations Committee that the U.S. is not negotiating a "legally binding plan," but one that has "a capacity for enforcement."

Forty-seven U.S. Republican Senators warned Monday in an open letter to Iranian leaders that a deal over Iran's nuclear program will be at risk once President Barack Obama leaves office.

"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 read.

The rare move of Congressional intervention on U.S. foreign policy drew criticism from the White House, with Vice President Joe Biden dismissing it as "a dangerous mistake to scuttle a peaceful resolution" of the Iran nuclear issue.

The P5+1 group, consisting of the U.S., Britain, France, China, Russia and Germany, is negotiating with Iran over its nuclear program in hopes of reaching a framework deal by the end of the month. The deal would likely oblige Iran to cut back its nuclear program -- reportedly for at least ten years -- in exchange for a loosening of crippling economic sanctions.

On Wednesday, Kerry said his reaction to the letter was "utter disbelief", adding that it "ignores more than two centuries of precedent in the conduct of American foreign policy."

"During my 29 years here in the Senate, I never heard of nor even heard of it being proposed anything comparable to this," said the U.S. top diplomat.

He also warned that the Republican Senators' move could harm global trust in the United States.

"This risks undermining the confidence that foreign governments, in thousands of important agreements, commit to between the United States and other countries," he said.

Many members of Congress are concerned that the Obama administration will sign off on a deal that is not strict enough, or that only delays Iran's ability to get a nuclear weapon.

Republicans and several Democrats have drafted legislation aimed at forcing Obama to submit the agreement to Congress, but haven't yet advanced the legislation for a vote. Endite