Twenty Maoists were gunned down during a combing operation by security forces in the border area of Nayagarh-Ganjam-Kandhamal districts of Orissa on Sunday.

Three jawans of the Special Operation Group were also killed in the operation being conducted since Saturday after the Maoist attack on police establishments in Nayagarh on Friday night, state Home Secretary T K Mishra told reporters in Bhubaneswar.

Some women Maoists were also among the 20 ultras killed in the exchange of fire.

Four policemen were missing in the continuing gunbattle between security forces and the militants, who killed 15 people on Friday, in the Ganjam-Kandhamal border area of Orissa, official sources said.

"Four of our personnel did not return to the base camp last night after the day's operation," Director General of Police Gopal Chandra Nanda said.

The intensive combing operation was launched on Saturday to track down the ultras who fled with a huge cache of arms and ammunition after killing 15 people, including 14 policemen, in daring attacks on several police establishments and armoury in Nayagarh on Friday night.

Confident that the Maoists involved in the strike would be neutralised, Mishra said the combing operation would continue till the end.

Besides the elite Greyhounds, the Central Reserve Police Force, Special Operation Group, state armed police and other security personnel were engaged in the operation launched simultaneously in three districts of Nayagarh, Kandhamal and Ganjam, he said.

Stating that top officers were directly supervising the operation, he said, "They have been told to continue the operation till the last man involved in the Nayagarh killing is nabbed or killed.