Excessive demands by the United States would be the main reason behind any failure in the nuclear talks, Velayati said in a televised interview with IRIB on Sunday.
Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany) are in talks to hammer out a lasting accord that would end more than a decade of impasse over Tehran's peaceful nuclear program.
On April 2, the two sides reached a framework nuclear agreement in Lausanne, Switzerland, with both sides committed to push for a final deal until the end of June.
Velayati, who is also an adviser to the Supreme Leader of the Islamic Revolution, reminded that American officials are dishonest and renege on their promises, adding that it is why Tehran insists on the necessity for immediate termination of the anti-Iran sanctions.
He further criticized the US war rhetoric, saying that their "military option" against Iran has become a laughing matter.
"If they were able to use the military option against Iran, they would not hesitate even for a moment," he added.