Raipur, July 12 - In one of the deadliest attacks since the government named CPI-Maoist as a terror outfit last month, leftwing ultras killed at least 20 policemen in an ambush in a forested stretch of Chhattisgarh state Sunday.

'A contingent of District Force (DF) and Chhattisgarh Armed Force (CAF) drove into a booby trap laid by Maoists in a thickly forested area in the state's western region of Rajnandgaon district in which 20-plus jawans were killed,' Pawan Deo, deputy inspector general (DIG) at the police headquarters here, told IANS.

He said District Superintendent of Police B.K. Choubey was among an unspecified number of the injured and battling for life but he refused to give further updates.

The attack took place in the Manpur belt of the district, bordering Maharashtra, and some 200 km from state capital Raipur.

It has shaken up the police force in the state that is hit by Maoist insurgency since the 1980s. All top officials including state police chief Vishwaranjan rushed to the attack site.

Chief Minister Raman Singh has cancelled his trip to Nagpur scheduled for Sunday afternoon and asked the home department to send choppers to rescue the injured policemen.