By Omer Farooq
BBC correspondent in Hyderabad
News Online looks at the People's War Group, linked to an attack that has left 26 police dead.
The People's War Group (PWG) was formed in 1980 by a school teacher, Kondapally Seetharamaiah, in southern India.
An outlawed group, it began as an armed peasant movement that advocated revolution in the Indian countryside
It is mainly active in Andhra Pradesh state but also has a presence in Orissa, Chhattisgarh and Jharkhand.
It has also developed links with other Maoist rebel groups in Bihar and Nepal.
The PWG was inspired by the Naxalbari movement of West Bengal - a student-led communist agitation of the late 1960s.
Seetharamaiah left his job at a school in Andhra Pradesh to become a left-wing activist.
He chose to follow the Maoist dictum of bringing about a "revolution from the barrel of a gun" and started recruiting men for his group.
The group then projected itself as the voice of the poor and landless and fought oppressive landlords.
But over the years, it graduated to a level where it started targeting the state and the security forces.
The PWG enjoys a stronger presence in areas which have seen little economic development and are dominated by dalits, or those on the lower rungs of the Hindu caste hierarchy.
An armed peasant movement based in the countryside
It draws much of its support from the landless poor. But critics say the majority of PWG victims too are poor.
The rebels, however, say they were killed because they were helping the police and security forces.
1987 was a turning point for the PWG when its activists kidnapped a group of senior bureaucrats.
The PWG also acquired sophisticated weapons and expertise in laying landmines around this time.
It declared an armed struggle against the government and demanded that an independent communist state be carved out of Andhra Pradesh and some neighbouring states.
In October 2003, the chief minister of Andhra Pradesh, Chandrababu Naidu, narrowly escaped a landmine attack blamed on the PWG.
The group declared several areas under its sway, calling them "guerrilla zones".
It still maintains several of these in the Telangana region of Andhra Pradesh, the Dandakarneya region in Chattishgarh and in Orissa.
Chandrababu Naidu narrowly escaped a PWG attack
It gained strength when another left-wing group - the Communist Party of India (Marxist Leninist Party Unity) - which was active in the state of Bihar - merged with the PWG in 1998.
The PWG also established links with the Maoist Communist Centre of Bihar and the left-wing rebels active in neighbouring Nepal.
While the group has since spread its area of influence to other parts of India - it is most active in Andhra Pradesh, Orissa, Chhattisgarh and Maharashtra.
There were reports that the group was in talks with other left-wing rebel organisations to try to establish a "revolutionary zone" from Nepal to Andhra Pradesh.
No one knows the exact strength of the group - but official assessments vary from a 600-strong cadre in Andhra Pradesh to about 3,500 across India.
But there has been a sharp decline in the quality of recruits recently.
While its revolutionary ideas used to attract educated professionals, the lure of money and power led many criminals to join the group in the 1990s.
The organisation now largely relies on extortion to fund its activities, reportedly collecting between five and $10m a year.