The jungle clash in central India erupted after a unit of 100 soldiers and armed police went to check on a suspected rebel camp only to find themselves heavily outnumbered and outgunned, security sources told AFP.

The estimated 500 guerrillas in insurgency-hit Chhattisgarh state were equipped with bullet-proof jackets and helmets, mortars, automatic weapons, rocket launchers and advanced improvised explosive devices.

"The security men had almost entered the rebel stronghold but heavy firing from every side stopped them," a Chhattisgarh police official told AFP on condition of anonymity.

"It indicates they are even prepared for an air strike or to counter tanks," said another senior top police official, who also requested anonymity.

Dozens of troops apparently ran away from the clash in the mineral-rich state's forested Dantewada district, 500 kilometres (310 miles) south of state capital Raipur.

Other police sources said troops ran out of ammunition while the Maoists quickly summoned reinforcements.

The debacle has prompted serious questions over how India is fighting the rebels -- described last year by Prime Minister Manmohan Singh as the biggest threat to the internal security of the world's largest democracy.

The guerrillas appear to enjoy massive support among the region's vast tribal population and landless farmers neglected by governments and fed up over unemployment and rampant corruption.

Originally a peasant uprising which erupted in 1967 in the eastern state of West Bengal, the rebellion has spread across 14 of India's 29 states. Chhattisgarh is now seen as the movement's nerve centre.

"You can't fight the challenge even with better weapons because the troops are heavily outnumbered and most are trained for static jobs -- not for guerrilla warfare," said Ajai Sahni, head of the Institute for Conflict Management.

Less than 2,000 counter-insurgency security forces have been deployed in Chhattisgarh against 4,500 armed Maoist cadres if the "most conservative estimate" is used, he said.

"If you take irregular forces on each side, the ratio of security forces to that of Maoist fighters is 1:10," he said, adding the rebels were seeking to make a part of the state their first "liberated zone."

The state government has drafted civilians into police but Sahni called this "immoral."

Locals can be involved "when police dominance has been established, not as a forward force," he said.

"There are enough resources" to deal with the problem, he added, but blamed "lack of will."

Chhattisgarh police said the incident has led to a serious security review -- although similar action was promised in March when 55 policemen were killed in the worst-ever Maoist assault in the state.

"We're reorganising our forces," said Inspector General of Police RK Vij, without elaborating.

Security analyst PV Ramana said government forces, helped by good intelligence, managed to get the Maoists "on the run" in southern Andhra Pradesh state, which was worst hit by the rebels.

But Ramana said the new Maoist attacks in Chhattisgarh are the "mere beginning of what they envisage launching."

Better intelligence and training are needed to deal with "battle-hardened guerrillas," he said, adding: "This is going to take some time."