The explosion occurred near Puridih Dam, 240km from the Jharkhand state capital Ranchi.

 

Jharkhand is a known hotbed of the Maoist insurgency which grew out of a peasant uprising in 1967.

 

'Security threat'

  

The Maoist fighters are active in over half of India's 29 states and use a heavily forested region in the state of Chhattisgarh as their headquarters.

  

Manmohan Singh, the Indian prime minister, has described the Maoists as the biggest threat to India's internal security.

  

At least 834 people were killed in Maoist-related violence nationwide last year.

 

New Delhi has refused to hold peace talks with the Maoists unless they renounce violence.

  

Analysts say the government needs to focus on improving living conditions in India's impoverished hinterland as part of its strategy to combat the rebels.