Police say at least 20 Maoist rebels have been killed in clashes with security forces in central India.

The gunbattle took place overnight in Chhattisgarh state after paramilitary and police forces launched an operation there late Thursday.

Police say six paramilitary soldiers were wounded in the encounter, including two with critical injuries. They were airlifted to a hospital in the state capital, Raipur.

Officials say the operation is continuing, with more security personnel deployed to the forested area to clear it of rebels.

India's government has repeatedly called the Maoist rebels one of the biggest threats to the country's internal security. More than 1,000 people were killed in rebel violence in 2010.

The rebels say they are fighting for the rights of the poor and landless against what they say are severe inequities in land acquisition and wealth distribution.

While the number of Maoist attacks has decreased in recent months, the rebels have carried out several high-profile kidnappings — capturing two Italians, an Indian lawmaker and a district officer.

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