Up to 200 Maoist rebels ambushed a patrol of paramilitary troops in eastern India yesterday evening, killing 27 of them in their third major attack on security forces in as many months, according to local police. Another ten troops were wounded when the rebels attacked a 63-member patrol of the Central Reserve Police Force in dense forest in the state of Chhattisgarh, according to Sunder Raj, a senior local police official. The Maoists also known as Naxalites fought a 90-minute gun battle with the troops but fled after police reinforcements reached the remote area of Narayanpur district, which is considered a rebel stronghold, other police officials said. Paramilitary forces launched a fresh operation today to flush out the rebels as state and central government officials met to review their strategy for tackling what Manmohan Singh, the Indian Prime Minister, has called Indias biggest internal security threat. Many security officials are now calling for the Army and the Air Force to be deployed, but the Government is reluctant to use the Armed Forces against its own people, and military commanders are wary of getting sucked into a protracted civil war. The Air Force has agreed, however, to provide some logistical support, and the Government said last week that it was negotiating the return of 15 helicopters being used in UN missions in Africa. The Naxalites take their name from the village of Naxalbari in West Bengal where they first launched a peasant uprising inspired by the ultra-leftist ideology of Mao Zedong, the Chinese revolutionary leader, in 1967. They have since grown into a force of an estimated 20,000 full-time guerrillas who operate in a third of Indian districts, and control a red corridor between the east coast and the Nepalese border. Last year the Government launched Operation Green Hunt, an unprecedented nationwide campaign involving 60,000 federal paramilitary forces who were sent to help state police to tackle the rebels. But the Maoists responded with a series of audacious assaults that have exposed the weakness of the police and paramilitary forces, and prompted the debate over whether to use the Army and Air Force. At least 35 people were killed last month when the rebels detonated a landmine under a bus carrying police and civilians in the state of Chhattisgarh. In April, they killed 75 policemen in an ambush on the same area. They were also blamed for derailing a packed over night passenger train in West Bengal last month, killing at least 145 people, although they denied any involvement in that attack.