World Bulletin / News Desk 

Iran's Supreme Leader hit out on Thursday at a letter by U.S. Republican senators threatening to undo any nuclear deal between Washington and Tehran, saying he was worried because the United States was known for "backstabbing", Mehr news agency reported.

Ayatollah Ali Khamenei added in a speech to senior clerics that whenever negotiators made progress, the Americans became "harsher, tougher and coarser", Mehr reported. He said U.S. accusations of Iranian involvement in terrorism were risible.