In a massive operation against the Maoists, security forces have laid siege to a hill in Jharkhand, entrapping nearly 250 guerrillas by cutting their supply lines, police said in Ranchi on Friday.The 'Jaal Char' operation has been jointly launched by the state police and Central Reserve Police Force (CRPF) in Latehar district, around 145 km from the state capital Ranchi."The operation was launched 10 days ago in a well planned manner with around 2,000 security personnel now surrounding the hill. Gun battles took place at least on five days. We have cut the Maoist supply lines by deploying forces at Kumadih railway station," a police officer involved in the operation told IANS.Police claim to have killed at least eight Maoist guerrillas, destroyed one camp, seized landmines, explosives, mobile phones, medicines and other materials in the last 10 days of the operation.The hill is spread around 17 sq km. With more than 15 villages located in the area, the security forces are gradually closing upon the guerrillas, a police officer said.According to sources at the police headquarters here, the union home ministry has been informed about the operation.Earlier on Thursday, Jharkhand police chief Rajiv Kumar, who is monitoring the entire operation, said the Maoists should either surrender or be prepared to face bullets.According to police sources, some important Maoist leaders could be among those trapped by the security forces.Operations against them are going on in various parts of the state, including the Saranda forest in West Singhbhum and Palamau and Dumka districts where Pakur Superintendent of Police Amarjit Balihar was killed by the Maoists Tuesday.Maoist guerrillas are active in 18 of the state's 24 districts.