The ultras had joined Maoist-backed Chasi-Mulia Adivasi Sangh in 2009 and later became active members of the banned CPI(Maoist), they said.
"The rebels were trained in using different arms and planting landmines. We suspect their involvement in Maoist offensives at Narayanpatna and Laxmipur," IG of Police (South-Western range), Yashwant Kumar Jethwa said.
The Maoists, who surrendered yesterday, were also engaged in organising village meetings and worked as couriers, he said.