Maoist rebels in the eastern Indian state of West Bengal have attacked police camps and demolished the house of a local communist leader.
The bodies of four workers of the ruling Communist Party of India (Marxist) were recovered in the restive jungle region of Lalgarh.
A further four are missing. Police say they may have been killed or kidnapped.
Rebels have taken almost total control of Lalgargh in West Midnapore district since last November, reports say.
About 6,000 people have been killed in violence linked to Maoist rebels in India over the past 20 years.
They are active in states across east and central India - the so-called "red corridor". Last week more than 20 police were killed in the eastern state of Jharkand.
In the latest incident, rebels ransacked and torched at least three police camps after entering the Dharampur area of Lalgarh on Monday.
They also destroyed the house of a local communist leader who managed to flee his home, reports said.
The rebels have also made their presence felt in around 170 villages in Lalgarh, threatening supporters of the state's ruling communist party and warning them to leave the area, reports said.
The district has experienced unrest for a number of months.
Tribal people in Lalgarh launched violent protests and strikes against the police in the area last November.
The protests came shortly after former federal minister Ram Bilas Paswan narrowly escaped a landmine explosion set off by suspected Maoist rebels.
The BBC's Amitabha Bhattasali says that Lalgarh has remained under almost total control of the Maoists ever since then, with the police and administration virtually non-existent there.
At that time a serving police officer in West Bengal caused controversy by refusing to command a camp in district. He is reported to have told colleagues he would rather resign than risk his life.
Analysts say that Maoists operate in 182 districts in India, including some in West Bengal.
The rebels say they represent the rights of landless farmhands and tribal communities. They have attacked police outposts and enforced strikes in India's mineral heartland.
Indian Prime Minister Manmohan Singh has called the Maoist movement the "biggest threat to India's national security".