At least 25 people have been killed after Maoist rebels blew up two trucks carrying civilians in India's central state of Chhattisgarh, police say.
An anti-Maoist rally in Chhattisgarh
Senior state police official SK Paswan said the number of dead could rise. Many of the nearly 40 injured were in a critical condition, he told the BBC.
Details of the attack are sketchy. It happened in Dantewada district, 500km (300 miles) south of Raipur.
Police are hunting the rebels, who have said they carried out the attack.
Maoist rebels are active in about a third of India's states and are so powerful in several districts of central and eastern India that they virtually run a parallel administration.
They say they are fighting for more rights for indigenous people.
Police have sealed off the area while they search for the attackers, and civilians, including the media, are being kept out.
Earlier on Tuesday, a police officer close to the scene told the BBC the death toll was nearer 100, but this figure is not confirmed.
Senior Chhattisgarh officials held emergency talks after the attack.
The state's Home Minister, Ram Vichar Netam, said the two trucks had been blown up by landmines.
"Some people have also been kidnapped by the rebels," he told the BBC.
Mr Paswan said the injured had been taken to hospital in neighbouring Andhra Pradesh state by helicopter.
The victims were tribal people returning from a meeting called to protest against the Maoists' activities in the state.
The BBC's Alok Putul in Raipur says the area where Tuesday's attack happened is covered with landmines.
Our correspondent says that Maoists killed 40 people in Chhattisgarh in February, including 22 policemen.
Last September, all Maoist groups were banned in Chhattisgarh after 24 paramilitary police were reported killed in a landmine explosion in Dantewada district.
The Maoists also kidnapped a number of people, officials say
Two weeks ago the Chhattisgarh authorities said the rebels had killed three tribes people on suspicion that they were police informers.
Up to 20,000 people are living in temporary camps run by the state.
The government set up the camps after the authorities launched an operation against the rebels whom they accuse of killing and kidnapping villagers.
Maoist rebels have attacked one such camp recently in which eight people were killed.
Mr Netam has said that the security in the state is hampered by a shortage of policemen.
The Maoists have a strong presence in eight of 16 districts of the state.