Niger’s coup leaders on Thursday said that they had severed military ties with France, their country’s former colonial ruler, throwing into uncertainty the future of 1,500 French troops based there, in a region of West Africa plagued with coups and Islamist insurgencies. “You can’t just wake up in the morning, and with no reason, declare that you are the ruler,” Kiari Liman-Tiguri, Niger’s ambassador to the United States, said in an interview with The New York Times this week, before announcement that he had been dismissed by the military junta. Abdourahmane Tchiani, who claims to be in charge of Niger, said in a television address that he had seized power to restore security and fight corruption