YENAGOA, Nigeria, Sept 20 (Reuters) - Nigerian authorities imposed a communications blackout on Monday in several parts of Sokoto state as a crackdown against armed kidnappers in the country"s northwest region spreads. Gangs of armed men seeking lucrative ransom payments, known locally as bandits, have spread across northwestern Nigeria over the past year, kidnapping more than 1,000 students from schools and taking others from hospitals, homes and roads. Muhammad Bello, Sokoto state"s special adviser for media and publicity, said the state governor, in collaboration with the country"s Communications Ministry, had blocked communications services in 14 local government areas. The state earlier this month closed some roads to motorists, suspended animal trades and prohibited the transportation of more than three people on motorcycles as part of efforts to curb banditry, Bello said. Sokoto shares a border with Zamfara state, which has been one of the worst-hit states in a wave of mass abductions of students from schools by gangs of ransom seekers operating from remote camps. Zamfara was the first to impose a communications blockade earlier this month and officials there said some bandits escaping from an army crackdown had sought refuge in Sokoto.