India, May 7 -- At least 15 Maoists were killed in an encounter with security forces in Bijapur district of Chhattisgarh as part of a large-scale operation against ultras in the region, the police said on Wednesday.

Police said that the number could increase, and a search operation is underway.

"The encounter took place in the wee hours of Wednesday. According to preliminary information, 15 to 18 Maoists have been killed in the dense forests surrounding the Karregutta hills along the Chhattisgarh-Telangana border. A search operation is on, and more details will be provided in the next few hours," a senior police officer, who is reviewing the operation, said.

The massive operation, described as one of the largest counter-insurgency miss...