Iranian Supreme Leader Ayatollah Ali Khamenei has criticized a letter by Republican senators threatening to nullify any nuclear deal between Washington and Tehran.
Khamenei said in Tehran on March 12 that whenever progress is made between Iran and the six world powers negotiating a deal to curb Tehran's controversial nuclear program, U.S. officials become "harsher, tougher, and coarser," Iran's Mehr News Agency reported.
In reference to the March 9 open letter to Iranian leaders signed by 47 U.S. Senate members, Khamenei added that the United States is known for its "deceit and backstabbing."
The senators warned in the letter that any nuclear deal made with U.S. President Barack Obama could be changed after he left office in 2017.
Talks aimed at reaching a deal that would grant Iran relief from international economic sanctions if it limits its nuclear program, which Western nations fear could be a front for nuclear weapons development, resume in Switzerland next week.
Negotiators are seeking a framework agreement this month and have set a June 30 deadline for a full deal.