The rebel Liberation Tigers of Tamil Eelam set off the mine, planted near an electricity transformer, targetting a bus taking constables home on leave, a ministry spokesman said.
Heavily armed Naxals on Monday ambushed a Central Reserve Police Force patrol party in the jungles along the Chhattisgarh and Maharashtra border resulting in exchange of gunfire between the two sides.
A dozen Maoists were possibly killed during the encounter in Jharkhand's West Singhbhum in which six security personnel were injured, a senior police officer said on Monday.
The bus toppled and was dragged about 25 metre before it came to a halt after being hit by the powerful blast.
The mine, planted near an electricity transformer, was targeted at a bus taking constables home on leave, a police official said.
Wali, who returned from Sri Lanka a week ago, alleged that the attack was carried out by RAW to begin a proxy war in a third country.
The blast is supposed to have been triggered by an army unit.
As many as 18 soldiers were killed in Puloly in two similar attacks early in December.
According to a report in The Hindu, the Indian Army carried out surgical strikes across the LoC in August 2011 in retaliation for a surprise attack on an army post in Kupwara in July 2011 that killed six soldiers.
Extra security measures will be in force for these areas in the period between June 10 and 14.