As regards the best approach to deal with the enemy's hostile moves, Ayatollah Khamenei said Iranian authorities should prove it to the "corrupt leaders of the USA regime" that they rely on the Iranian nation who would never bow to force.
Iranian Supreme Leader Ali Khamenei threatened Washington on Sunday, saying: "Iran will respond to every wrong step by the United States regarding the nuclear deal".
Washington extended some sanctions relief for Iran on Thursday under Tehran's 2015 deal with world powers but said it had yet to decide whether to maintain the agreement.
President Hassan Rouhani left on Sunday for the UN General Assembly in NY, where he is set to hold crucial talks on the 2015 nuclear deal, which eased global sanctions in exchange for curbs to Iran's atomic programme.
"Today, despite all the commitments and discussions in the negotiations, America's attitude towards these negotiations and their outcome is completely unjust and amounts to bullying", Khamenei said.
"All the wrong steps by the domineering regime regarding the JCPOA will lead to a corresponding reaction from the Islamic Republic", Khamenei said, as quoted by the Islamic Republic News Agency.
After years of tension with the West, Iran struck a deal with Britain, China, France, Russia and the U.S. plus Germany in July 2015, under which Iran agreed to limit its uranium-enrichment activities in return for the lifting of western and worldwide sanctions.
Iran denies its missile development breaches the resolution, saying its missiles are not created to carry nuclear weapons.