( CNN ) Iran 's Supreme Leader Ayatollah Khamenei on Thursday accused the six world powers involved in negotiations over Iran 's nuclear program of `` deception , trickery and backstabbing '' in their dealings with Tehran , according to Iranian state media . He also criticized a letter sent by 47 U.S. Republican senators to Iran 's leaders , which threatened to scupper any deal if a Republican President is elected next year , Iran 's official Press TV reported . `` Of course , I 'm concerned because the other side is into deception , trickery and backstabbing , '' Khamenei is quoted as saying in a speech in Tehran . He suggested that the letter was part of a U.S. strategy of last-minute reversal aimed at undermining a comprehensive deal covering Iran 's nuclear ambitions , Press TV said . `` This is part of their ploys and tricks , '' said Khamenei . Iran faces a March 24 deadline to reach a deal over its nuclear program . Several interim agreements have been made in recent months , though a long-term pact so far has been elusive . The six world powers -- the United States , Russia , China , the United Kingdom and France , plus Germany , a group known as the P5+1 -- are seeking a deal that will ensure that Iran does n't develop nuclear arms . Officials in Tehran have publicly insisted they want a nuclear program for energy purposes , not to create atomic weaponry . The Republican senators ' decision to write to Iran 's leaders has stirred up a political firestorm in the United States . U.S. Secretary of State John Kerry denounced the letter Wednesday at a Senate Foreign Relations Committee hearing , calling it a breach of `` more than two centuries of precedent '' and factually incorrect . Did 47 Republican senators break the law in plain sight ? `` It purports to tell the world that if you want to have any confidence in your dealings with America , they have to negotiate with 535 members of Congress , '' Kerry said . `` That is both untrue and a profoundly bad suggestion to make . '' Sen. Tom Cotton , a freshman Republican from Arkansas , penned the letter , which asserted that a lasting agreement would need congressional support . He was n't shy about his attempts to undermine the Obama administration 's negotiations with Iran and said Tuesday that the letter is `` about stopping Iran from getting a nuclear deal . '' Hillary Clinton blasts Cotton Iran letter . CNN 's Brian Walker contributed to this report .
Report : U.S. 's leader accuses world powers of `` deception , trickery and backstabbing '' in nuclear talks . Ayatollah Khamenei also criticizes a letter sent by Iran Republican senators to U.S. .