(Adds details, revises death toll)
By Jatindra Dash
BHUBANESWAR, India, March 11 (Reuters) - Maoist rebels ambushed police and killed 16 involved in a mine clearing operation in a remote part of eastern India region on Tuesday, police said, as the insurgents demonstrated their strength ahead of a general election next month.
The victims were clearing mines laid by rebels on a road through a densely forested area in resource-rich Chhattisgarh state when the rebels attacked from all sides, according to a senior home ministry official.
The head of anti-Maoist operations in the state police force told Reuters one civilian was among the dead.
"Total death 16 ... including one civilian," R.K. Vij said in a text message sent from a helicopter after the attack. However, there were conflicting accounts of the death toll, with other officers telling local media at least 20 died.
Television images from the site showed a heavy truck smouldering with its tires burning.
The rebels have operated for decades across a wide swathe of central and eastern India, and grew in strength during recent times in areas where poor, tribal villagers came into conflict with mining companies seeking resources for industralisation.
The Maoists seek the violent overthrow of the Indian state but have so far not managed to spread significantly into urban areas. Attacks picked up slightly for the first time last year peaking in 2010.
"They attack us to demoralise us, they attack us to loot our weapons," said the ministry official, who asked not to be named.
The ambush was just a few miles from where rebels killed 27 people, including many senior political leaders, before state elections last year. The attacks seek to disrupt the electoral process, the official said.
"This time they know if we succeed in elections it will dent their reputation," he said.
Prime Minister Manmohan Singh has previously described the Maoist insurgency as India's biggest internal security challenge. (Additional reporting by Sruthi Gottipati in New Delhi; Writing by Frank Jack Daniel; Editing by Douglas Busvine and Simon Cameron-Moore)