At least three policemen have been killed in a landmine blast in India's eastern Orissa state, police say.
The dead included Bhupinder Singh, deputy commandant of the elite paramilitary force, Central Reserve Police Force (CRPF).
The attack took place in Malkangiri district where Maoist rebels control large swathes of territory.
They have have also abducted a former legislator in the eastern Indian state of Jharkhand, police say.
Ramchandra Singh, a leader of the Rashtriya Janata Dal (RJD) party, was kidnapped by a group of armed rebels in Latehar district on Thursday night.
Police say the Maoists have not yet put forward any demands for his release.
Mr Singh was canvassing for the forthcoming state assembly elections. Polls are to be held in five phases between 27 November and 18 December.
"The security personnel were on their way from their camp in Kalimela to Comapagunda, possibly to buy rations, when the blast occurred," Malkangiri superintendent of police Satyabrata Bhoi told the BBC.
The incident occurred at about 8am (0230GMT) near a known stronghold of Maoist rebels.
The landmine, planted under a culvert, went off when the van carrying the security personnel passed over it.
Mr Bhoi said additional troops had been sent to the area.
Officials say the attack is an effort to deter and demoralise security forces ahead of their planned offensive against the Maoist rebels in the area.
Home Secretary GK Pillai is due in Orissa next week to give a final shape to the operation - named "Operation Godavari" - after discussions with the state government.
The BBC's Sandeep Sahu in Bhubaneswar says that Maoists have intensified their operations in their stronghold of south Orissa in recent days.
Indian Prime Minister Manmohan Singh has described the Maoist insurgency as the single largest threat to the country.
The Maoists have a presence in more than 223 of India's 600-odd districts across 20 states, according to the government.
The rebels say they are fighting for communist rule and the rights of the poor peasants and landless. More than 6,000 people have died during the rebels' 20-year fight.
There has been a surge in Maoist violence in recent months - the rebels have kidnapped and killed policemen, help up an express train, attacked police stations, and blown up railway lines and communication links in affected states.