Iran's Ayatollah Khamenei was highly critical of a letter sent by U.S. Republicans to Iran's leadership. Reuters/Stringer

Iran’s Supreme Leader Ayatollah Ali Khamenei responded to a controversial letter sent to Iran’s leadership by a group of 47 U.S. Republicans that critics say was in poor taste and subverted delicate negotiations over Iran’s nuclear program in Geneva with the P5+1 and Iran.

The letter was led by freshman Republican Sen. Tom Cotton of Arkansas, who said he and the other 46 signers of the letter sought to “educate” Iran’s leaders on the U.S. Constitution and that any incoming president could easily cancel any deal made by President Barack Obama, which the White House said was inaccurate. Congress traditionally has kept any partisan disagreements over treaties within U.S. borders so as not to project political divisions abroad.

Khamenei called the letter evidence that the U.S. is deceptive in negotiations, adding that it indicates political ethics have collapsed in the U.S.

“Every time we reach a stage where the end of the negotiations is in sight, the tone of the other side, specifically the Americans, becomes harsher, coarser and tougher. This is the nature of their tricks and deceptions,” Khamenei said, according to Al Aribaya, adding that he was worried because the U.S. “is known for opacity, deceit and backstabbing.”

Cotton and his Republican colleagues received harsh criticism at home and abroad for the letter, as some more fervent critics called it treasonous and petty. Iranian Foreign Minister Mohammad Javad Zarif said it “has no legal value and is mostly a propaganda ploy” in a statement earlier this week, and that it was “unprecedented in diplomatic history,” according to the Fiscal Times.

German Foreign Minister Frank-Walter Steinmeier also was critical of the letter, saying it affects the negotiations negatively and builds mistrust. He said it would good “if the letter ... no longer causes any disturbance in the negotiations,” according to Agence France-Presse. Sen. John McCain, the ranking Republican on the letter, brushed off Steinmeier’s comments, saying he didn’t “have any credibility in any way to me” because of Germany’s stance on Ukraine.