Bhubaneswar, April 27: Vigil has been stepped upOdisha's border with Chhattisgarh in the wake of the killing of 25 CRPF jawans in a Maoist ambush on Monday in the neighbouring state's Sukma district.

DIG of police, south-western range, S. Shyny said combing had been intensified on the border to ensure that rebels from Chhattisgarh did not sneak in. "Our effort is to ensure that Maoists don't enter our area. We are taking all security precautions," she added.

The most sensitive districts of Odisha are Malkangiri and Koraput, both of which share borders with Chhattisgarh and are known rebel strongholds. Rebels from this region had taken part in the May 25, 2013, attack on a Congress convoy in Chhattisgarh's Darbha valley in which several Congress leaders had been killed.

In another development, CPI (Maoist) Dandakaranya zonal committee spokesperson Nikhil today released an audiotape justifying the Sukma attack. He also cautioned the security forces against targeting innocent people.<>

Senior police officers, who did not wish to be quoted, said Odisha districts like Malkangiri and Koraput should be on constant alert given the strong presence of rebels there. On February 1 this year Maoists had triggered a blast in Koraput's Sunki valley killing eight police personnel. In the same area they had also detonated an indigenous explosive device (IED) in 2013 blowing up a BSF vehicle leading to the death of four jawans.

State police, however, had a major success against the rebels on October 24 last year when they gunned down 24 Maoists including six women cadres on Odisha-Andhra Pradesh border. Munna, the son of top rebel commander, Ramakrishna, was among those killed in operation that was carried out with the help of AP police. Eversince Maoists are in revenge mode.