At least 20 people, including policemen, were feared killed when suspected Maoist rebels detonated a landmine under a bus in central India today, local media reported.
Television news channels said 25 were killed, and one report said up to 50 people could died.
Police and government officials confirmed the attack but could not provide details on casualties.
The attack occurred in Dantewada area in Chhattisgarh state, said to be the worst hit by the four-decades-old insurgency that has killed thousands of people and has been described by the government as India's gravest internal security threat.
The attack was the worst since an April strike by rebels in which at least 75 policemen were killed in the same region.
The Maoists regularly attack railway lines and factories, aiming to cripple economic activity. With the rebels controlling vast swathes of mineral-rich areas, the government has often struggled to transport coal to power and steel companies.
Recent attacks on police have raised questions over how well prepared security forces are to tackle the Maoists, especially during a counter-offensive by security forces this year.
Reuters