Secretary of State John Kerry in the Egyptian resort of Sharm el-Sheikh on March 13, 2015. He said the open letter by Republican senators to Iran's leadership contained "false information." (Brian Snyder/Pool via AP)

Secretary of State John Kerry called the open letter penned by 47 Republican senators to Iran's leaders over negotiations on that country's nuclear program "absolutely calculated," "unprecedented" and "unthought-out."

"It's false information and directly calculated to interfere and basically say, 'Don't negotiate with them, you've got to negotiate with 535 members of Congress.' That's unprecedented. Unprecedented," Kerry said in an interview Sunday with CBS News.

Kerry's comments came a day after White House chief of staff Denis McDonough wrote a letter to Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) warning Congress not to interfere in the negotiating process.

"We agree that Congress will have a role to play — and will have to take a vote — as a part of any comprehensive deal that the United States and our international partners reach with Iran," McDonough wrote in the letter, first reported by the Huffington Post. But he said legislation that Corker has sponsored goes "well beyond ensuring that Congress has a role to play in any deal with Iran."

"Instead, the legislation would potentially prevent any deal from succeeding by suggesting that Congress must vote to 'approve' any deal," McDonough wrote.

Kerry echoed McDonough's comment. He added that the letter and legislation are premature. Also, he said, Congress has been briefed on the issue over 205 briefings, phone calls and discussions — 119 of them since January.

In the letter, written by Sen. Tom Cotton (Ark.), Republican senators suggest that any deal between the Iranian leadership and President Obama would be considered only an "executive agreement" that can be undone by future administrations or by Congress.

When asked whether he plans to apologize to international leaders over the letter, Kerry said: "Not on your life. I’m not going to apologize for the -- for an unconstitutional and unthought-out action by somebody who’s been in the United States Senate for 60-some days. That’s just inappropriate. I will explain very clearly that Congress does not have the right to change an executive agreement."

Cotton defended the letter on CBS News after Kerry's interview.

Freshman Republican Sen. Tom Cotton told CBS News he stands behind his letter to Iran, saying it is critical to stopping them from getting a nuclear weapon. (Reuters)

Asked why he decided to try to persuade Iranian leaders directly rather than writing an open letter to the American public, Cotton said that Obama is "negotiating a deal that is going to put Iran on a path to a bomb" and that Iran needed to hear directly from congressional leaders.

"Iran's leaders need to hear the message right and clear. I can tell you they are not hearing the message from Geneva,"  the site of negotiations with Iran, Cotton said.