Suspected Maoist rebels have killed six Indian police officers in central India.

Friday's attack took place in the Bastar district of Chhattisgarh, one of the states worst affected by the Maoist insurgency.

Police say at least three other officers were wounded when the rebels opened fire on 16 policemen traveling on motorcycles.

The police officers were returning from a village where rebels had reportedly carried out another attack.

Maoist rebels, known as Naxalites or Naxals, have infiltrated more than 20 Indian states.

Indian leaders have referred to Naxalism as the country's biggest internal security threat. The groups include some of the country's most extreme poor, who say they are struggling against state-sanctioned acquisition of their land and natural resources.

The rebels are widely seen as terrorists. Thousands of civilian and police deaths in India are blamed on Naxal attacks since the groups emerged in the late 1960s.