At least three security personnel were killed and six others injured, four of them critically, in a fierce encounter with Maoists in Orissa's Gajapati district early on Wednesday, the police said.

Acting on a tip-off, a team of security personnel including the elite anti-Naxal Special Operation Group and the state police had launched a combing operation in Ambajari forest near Paralakhemundi in Orissa in the wee hours of Wednesday.

A group of Maoists suddenly opened fired at the security personnel, who retaliated.

In the exchange of fire, three SOG jawans were killed and six others injured, the police said, adding four jawans were shifted to Vishakhapatnam as their condition was stated to be critical.

The dead were identified as Sanjeet K Tirkey, Balram Pradhan and Deepak Sonbhoy, while it is not yet ascertained that there was any casualty from the Maoist side, the police said.

The forest area, barely 5 km from this district headquarter town, was being thoroughly searched after the gunbattle to arrest the Naxals who fled, police said.

In another incident in nearby Malkangiri district, Maoists blew up a pump house and control room near the pipeline of a private industrial house meant for movement of minerals in Chitrakonda area, the police said.

About 50 armed Ultras raided the area and triggered explosion after overpowering and assaulting the guards present at the site, they said.