Maoist rebels have killed at least 70 police by setting off explosives and firing from hilltops around dense forest in central India.
At least two dozen have been injured in Chhattisgarh state on Tuesday in one of the worst attacks by the insurgents in years.
Reinforcements trying to collect bodies came under fire by the Maoists who have surrounded the area, Reuters reports.
The Maoists regularly attack railway lines and factories, aiming to cripple economic activity in many of the mineral rich and remote mining regions of India.
The attack echoed a similar ambush in February, when Maoists caught police off-guard in an attack on in the state of West Bengal, killing at least two dozen police.
Maoists have stepped up attacks in response to a police offensive that began last year in several states, which Indian officials say has for the first time weakened the decades-old movement.
The rebels, who say they are fighting for the rights of poor farmers and landless labourers, are trying to expand their influence in east, central and southern India.
Thousands have been killed in the insurgency which began in the late 1960s.
