ITANAGAR, April 3 ? Congress Chief Minister Mukut Mithi has written a letter to Prime Minister Atal Behari Vajpayee urging him to prevent the underground faction of National Socialist Council of Nagaland led by Isaac Muivah from climing that most tribals in the Arunachal Pradesh were Nagas, reports PTI. Government spokesman Takam Sanjoy told newsmen today that Mithi had informed his cabinet about the letter yesterday at a meeting. The NSCN(IM), he said, had claimed in printed material circulated that most tribals in Arunachal were Nagas, he said. He said, Arunachal Governor Arvind Dave had also recently requested the Centre for development of more security forces in Tirap and Changlang districts to check activities of both factions of the NSCN. A copy of the Governor?s letter was also sent to Lt. Gen H R S Kalkat, GOC-in-C of Eastern Command, he added.