Suspected Maoist rebels killed at least 19 people in Chhattisgarh when they ambushed a convoy carrying regional leaders from the ruling Congress party in dense forest on Saturday, officials said, one of the deadliest such attacks in recent years.
The rebels felled trees to block the 20-car convoy and then detonated a landmine and raked the vehicles with gunfire, Indian media reported.
Among those killed was Mahendra Karma, a senior Congress leader from Chhattisgarh who founded an anti-Maoist group and was believed to be the main target of the attack. The state's Congress party leader and his son were also killed.
Senior Chhattisgarh police official Mukesh Gupta told Reuters by telephone six policemen were among the dead and that 35 people were also wounded in the ambush.
Police had earlier put the death toll as high as 27 but that had been revised down, Gupta said.
Prime Minister Manmohan Singh condemned the attack and said his government would take firm action. Singh, who flew to Chhattisgarh with Congress party chief Sonia Gandhi on Sunday, has called the Maoists the greatest domestic threat to India.
The rebels, also known as Naxals, have fought for decades in a wide swathe of central and eastern India, including many resource-rich regions where tensions run high between poor farmers and industrial developers.
They are estimated to number between 6,000 and 8,000 hardcore fighters in nearly a third of India's 630 districts. While they have made few inroads into cities, they have spread into rural pockets in 20 of 28 states.
Maoists say they are fighting for the rights of poor farmers and landless labourers. Thousands have been killed in the insurgency since the late 1960s.
In the worst previous Maoist attack, an ambush by hundreds of rebels killed 75 policemen in Chhattisgarh in 2010.
Television reports said scores of rebels trapped the convoy in a forest in the Bastar region of Chhattisgarh, about 340 km (210 miles) south of the state capital Raipur, on Saturday. The Congress politicians had been returning from a rally.
"When our cars reached a turning point, the Naxals started firing. Two cars were blown up and the firing continued for almost one-and-a-half hours," NDTV quoted an injured Congress party worker as saying from hospital.