Monday's blast blew the bus to pieces
India's government is reviewing its strategy for fighting Maoist rebels after a landmine attack in Chhattisgarh state killed more than 30 people.
Most of those killed in Monday's blast, which destroyed a bus, were civilians, and the government is under pressure to take a tougher line against the rebels.
Home Minister P Chidamabaram wants a larger mandate, thought to include the use of air power to fight the Maoists.
Thousands have died in the rebels' decades-long fight against the state.
Meanwhile, a two-day strike called by the rebels in protest at an offensive against them is affecting life in parts of central and eastern India.
In Jharkhand, transport has been disrupted and many shops and banks closed. Security on trains has been tightened to avoid possible attacks.
Officials in West Bengal state say police reinforcements have been deployed in parts of Midnapore district, a Maoist stronghold.
Monday's attack on the bus in Chhattisgarh state's Dantewada district has prompted widespread anger in India, says the BBC's Chris Morris in Delhi.
Dantewada was the scene of the rebels' deadliest attack, when 75 paramilitary troops and their driver were killed last month.
In the past, the Maoists have warned civilian bus companies not to transport local police or members of the security forces.
In this incident it appears that Maoist supporters saw that armed police were on board the bus, and an attack was organised extremely quickly.
Our correspondent says it shows how powerful the Maoists have become in remote regions like the forests of southern Chhattisgarh. The government says it also demonstrates their barbarity.
Following the attack, the home minister said he would request wider powers to deal with the rebels.
"I took to the cabinet committee the case for a larger mandate. I was given a limited mandate. Now we will go back to the cabinet committee to revisit that mandate," Mr Chidambaram told the NDTV channel.
He said the chief ministers of some of the worst-affected states had asked for air power to be used against the rebels - a measure that the government has so far refused to sanction.
Our correspondent says the Defence Ministry does not want the armed forces involved in an internal security issue, however serious the threat may be.
At the moment the campaign is in the hands of local and federal paramilitary police forces.
'Rights of the poor'
The government's offensive - widely referred to as "Operation Green Hunt" began last October.
It involves 50,000 trooops and is taking place across five states - West Bengal, Jharkhand, Bihar, Orissa and Chhattisgarh.
The Maoists, also known as Naxalites, say they are fighting for the rights of rural poor who have been neglected by the government for decades.
But correspondents say support has been slipping away from the rebels, particularly after last month's attack.
The Maoist insurgency has been described by Prime Minister Manmohan Singh as the country's biggest internal security threat.
ministers in Delhi have always accepted that there is a need to tackle the root causes of the rebellion, such as poverty and the absence of effective local government.