Kerry tells Republicans: you cannot modify Iran-U.S. nuclear deal

WASHINGTON (Reuters) - U.S. Secretary of State John Kerry told Republicans who control Congress on Wednesday they would not be able to modify any nuclear agreement struck between the United States and Iran.

Kerry said he responded with "utter disbelief" to an open letter to Iran on Monday signed only by Republican senators that said any deal would only last as long as U.S. President Barack Obama, a Democrat, remains in office.

"When it says that Congress could actually modify the terms of an agreement at any time is flat wrong," Kerry, who has been negotiating a deal to rein in Iran's nuclear program in exchange for easing sanctions, told the Senate Foreign Relations Committee. "You don't have the right to modify an agreement reached executive to executive between leaders of a country."

But Sen. Rand Paul, a possible Republican presidential candidate in 2016, told Kerry that any deal would need approval by Congress if it affected U.S. sanctions against Iran. Paul accused the Obama administration of trying to bypass Congress.

"The letter was to Iran but it should've been cc' d to the White House because the White House needs to understand that any agreement that removes or changes legislation will have to be passed by us," the senator said.

The White House has described the letter as "reckless" and "irresponsible," saying it interfered with efforts by six major powers to negotiate with Iran and prevent it from building a bomb.

The negotiations, which resume in Lausanne, Switzerland, next week, are at a critical juncture as the sides try to meet an end of March target for an interim deal, with a final deal in June.

"We have been clear from the beginning, we are not negotiating, a quote, legally binding plan, we are negotiating a plan that will have in it capacity for enforcement," Kerry said. "The letter erroneously asserts this is a legally binding plan. It is not. We don't even have diplomatic relations with Iran."

"It is incorrect when it says that Congress can actually modify terms of an agreement at any time. That is flat wrong," Kerry said.

After the hearing Sen. Bob Corker, a Republican from Tennessee and chairman of the committee, said: "I want to follow up a bit on what he meant by that."

The letter was an unusual intervention by lawmakers into foreign policy, which is mainly the responsibility of the president's administration.

(Additional reporting by Patricia Zengerle; Editing by Doina Chiacu and Grant McCool)