How big a threat are the Maoist rebels in India?
Maoist rebels in India have killed 10 government supporters in West Bengal state this week and declared a "liberated zone" close to the city of Kolkata, sparking unease among investors in the communist-ruled state.
The attacks by the rebels, who are fighting for the rights of poor farmers and the disenfranchised, are among the most brazen in years.
Who are the Maoists?
The rebels began an armed struggle with a peasant revolt in Naxalbari village in West Bengal in 1967 but were initially crushed by the Congress-led government. After regrouping in the 1980s, they began recruiting hundreds of poor villagers, arming them with bows and arrows and even rifles snatched from police.
Indian authorities say they are led by Koteshwar Rao, also known as Kishanjee, who is in charge of militant activities, and Ganapathi (one name), the political leader. Neither have been seen in public and remain hidden in dense forest bases.
How big is the movement?
The rebels have an estimated 22,000 combatants in more than 180 of the country's 630 districts. They operate across a "red corridor" stretching from the southern state of Andhra Pradesh to the central state of Chhattisgarh and into West Bengal.
How big a threat are they to India's stability?
Prime Minister Manmohan Singh has described the insurgency as the biggest internal security challenge since independence. More than 1,000 attacks were recorded in 2008, as the Maoists targeted politicians, police and villagers suspected of being informers.
Authorities say the Maoists have a well thought-out plan to spread their influence into urban areas. Some of their recent attacks have been closer to cities and the latest strike in West Bengal is a show of their capability. Others say their influence will not extend far beyond remote rural areas.
What about the economy?
The Maoists regularly attack railway lines and factories, aiming to cripple economic activity. Their base in the "red corridor" gives them control of some of India's mineral rich areas.
The guerrillas could feed off the resistance in parts of rural India, including in West Bengal, against rapid economic growth that excludes hundreds of millions of poor.
The rebels advance to Lalgarh in West Bengal is near the construction site of a $7 billion steel plant by India's third largest steel producer, JSW Steel Ltd, which is watching how the government tackles the violence.
It could potentially scare off prospective investors from setting up shops in and around the Maoists' sphere.
How do the Maoists get arms?
They are in touch with other militant groups operating in India, including groups in Kashmir and the northeast, who help them. Police say they are equipped with automatic weapons, shoulder rocket launchers, mines and explosives.
What is the government's response?
The government has deployed hundreds of state and federal police to West Bengal to halt the Maoists' advance, but so far has refused to send in the army.