The attack came less than 24 hours before a rally scheduled in the Jharkhand city of Hazaribagh by Deputy Prime Minister Lal Krishna Advani ahead of national elections.

The police were killed late Wednesday when their cars hit a "string of mines" as they passed near Chaibasa in the Saranda forest, a popular tourist retreat 150km south of the state capital Ranchi, inspector general of police G.S. Rath said.

The 26 policemen killed were among a 150-member security patrol called to the area to probe reports that insurgents had raided a village, Rath said.

Chaibasa police chief Praveen Kumar, who was away from the site of the blasts, was found later with bullet wounds to his legs and was in critical condition, Rath said.

"Kumar was leading one of the two police parties which had gone for patrolling when the incident occurred," Rath said.

Jharkhand police chief R.R. Prasad blamed the attack on the outlawed Maoist People's War Group, one of several armed peasant movements which hold sway in large parts of the mineral-rich state.

It was the deadliest ambush by Maoists since the mountainous state was carved out of Bihar state in 2000.

Thousands have died since the 1960s in rural India in uprisings by militants claiming to fight on behalf of the poor against police and wealthy landowners.

In another attempted attack late Wednesday in Jharkhand, suspected Maoists tried to blow up an inter-city train near the city of Jamshedpur by taking out part of the track, police said.