LONDON - 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, is 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 Rouhani, 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 Islamic Revolutionary Guards Corps a foreign terrorist organization. Iran called the move "vicious" and vowed to retaliate.