Iran has appointed career diplomat and former nuclear negotiator Majid Takht Ravanchi as its envoy to the United Nations, state media said, as it tries to salvage a nuclear deal with world powers despite Washington's unilateral withdrawal. Takht Ravanchi, 61, was currently Iranian deputy foreign minister for European and American affairs. He has also served as ambassador to Switzerland. His move to the United Nations is significant since he was one of the negotiators who helped Tehran reach a nuclear agreement in 2015 with the United States, Britain, France, Russia, China and Germany. The pact curbed Iran's nuclear program in exchange for relief from international sanctions. However, US President Donald Trump last year pulled the United States out of the deal, which was concluded before he took office, saying it favored Iran. Other co-signatories are still trying to salvage the deal and shield Iran from US sanctions. President Hassan Rohani, who could be weakened by damage to Iran's economy if the deal falls apart, warned other signatories on Tuesday to honor their pledges before Tehran's patience runs out. On Monday, Trump designated Iran's Revolutionary Guards Corps a foreign terrorist organization. Iran called the move "vicious" and vowed to retaliate. Supreme Leader Ali Khamenei said: "They (United States) wish to plot against our Sepah (the Guards) ... it is in the frontline of confronting enemies of our (1979) revolution and has always defended the country ... America has failed to block our advancements." He was addressing a group of Guards. "In spite of all the pressure in the past 40 years, Americans have failed to do a damn thing and their vicious move will bear no fruit," he said. The head of Iran's Revolutionary Guards dismissed Washington's designation of the elite force as a terrorist organization and said on Tuesday the Guards would increase their military capabilities. — Agencies