NEW DELHI, India (CNN) -- At least 17 police officers were killed in what Indian authorities say was a shootout with Maoists Thursday.
The shootout occurred in a forest in the western state of Maharashtra, said Srihari Munde, a police official in the state's Gadchiroli district.
The officers were on a patrol when the assault took place, he said.
Indian Prime Minister Manmohan Singh has described Maoist rebels as the "gravest internal security threat" to India. He said last month that India's fight with them had fallen short of its objectives.
"I would like to say frankly that we have not achieved as much success as we would have liked in containing this menace," he told state police chiefs in September. "It is a matter of concern that despite our efforts, the level of violence in the affected states continues to rise."
The rebels have battled the government since the late 1960s. They claim to fight for the poor and dispossessed.
Maoists in India enjoy support not only from among the poorest and tribal communities, but also from some of the young and "intelligentsia," Singh has said.
"It still retains a certain elan. All this adds to the complexity of the problem," he said last month as he called for "better strategies" in dealing with armed Maoism.
The rebels have influence in 20 of the country's 28 states, according to the Indian government's latest assessment.
About 90 percent of Maoist attacks are believed to be carried out by the outlawed group known as the Communist Party of India (Maoist).
Last year, the country recorded a total of 1,591 Maoist strikes that left 721 people dead. In 2009, about 580 people have already lost their lives in 1,405 rebel attacks, the government says.
According to Indian Home Minister P. Chidambaram, Maoists have improved their military wares and operational tactics.
In addition to targeting police, alleged police informers and people they call "class enemies," Maoists are alleged to be putting greater emphasis on attacking economic and development infrastructure such as roads, bridges, railways, and power and telecommunication networks.
CNN's Harmeet Shah Singh contributed to this story.