In a major crackdown by CRPF, at least 20 naxalites, including a woman, were killed in a fierce overnight encounter in the dense jungles of Dantewada in Chhattisgarh that left six jawans wounded.

The encounter, which took place in the forests of Silger, an uncharted Maoist zone between the naxal hotbed of Jagargunda and Basaguda in Bijapur district of Bastar region, was launched last night in a joint operation by over 300 CRPF and state police personnel from three directions.

Seventeen bodies of the ultras have been recovered from the spot, Chhattisgarh ADG (Naxal Operations) Ram Nivas said, adding the combing operations were underway and the toll may rise. There were reports of three more naxals being killed.

Two Maoists, who were injured in the encounter, were apprehended and have been air-lifted for medical treatment to state capital Raipur, a senior CRPF official said.

This is the biggest offensive by the security agencies in the naxal stronghold in Chhattisgarh this year, the official said.

CRPF officials said two "prominent" naxals, operating in the Bijapur-Dantewada axis, were also killed in the encounter.

Six CRPF men, including two CoBRA commandos, sustained bullet injuries and have been air-lifted for medical aid to Raipur. Two of them are critical, he said.

This is the same area, close to Chintalnar, where naxals had carried out an audacious attack on security forces killing 75 CRPF men and one state police personnel in April 2010.

Keeping in view the tough terrain and presence of a big naxal squad in mind, the CRPF had deputed a Deputy Inspector General (DIG) and two Commandant rank officers, supported by an Additional SP of state police, to lead the operation.

The CRPF has mobilised three units of commandos and regular troops, aided by two helicopters for the encounter from three directions-- Jagargunda, Chintalnar and Basaguda.

Heavy exchange of gunfire took place between the two sides which continued till early morning, sources said.

The encounter comes over a month after Maoists had abducted and subsequently released the Collector of Sukma district--Alex Paul Menon, in Bastar region.

The CRPF has deployed about 20 battalions (20,000 personnel) for undertaking anti-naxal operations in the state.