New Delhi, July 13 - The killing of 29 policemen in Chhattisgarh, the epicentre of Maoist violence, has been the deadliest attack mounted by the rebels this year, demonstrating how they have expanded their grip in vast swathes of the state and beyond.

With 13 policemen, who were pressed into combing operations, still missing after Sunday's attacks, the security establishment in New Delhi has been shaken by the assault and is again re-examining the government's approach in dealing with left-wing extremism.

'Last month we have tried hard to follow our integrated approach of dovetailing policing with development works through a range of schemes of different ministries,' said a senior home ministry official.

'The deployment of the Commando Battalions for Resolute Action (CoBRA) in Chhattisgarh, we thought, would make a difference. Many areas in the state are still simply no-go areas.'

Till June this year, there have been 1,128 attacks in India's nine Maoist-affected states while there were 1,591 incidents in all of 2008. According to home ministry figures, at least 455 people had been killed in attacks by the Maoists in the first six months this year, with Chhattisgarh alone accounting for 148 deaths.

Though Sunday saw the biggest single casualty inflicted by the Maoists this year, the state has seen worse in the past. In March 2007, armed rebels killed 55 policemen in Bijapur block of Bastar district, one of the worst hit regions. Earlier, during the general elections this May, they hijacked trains and murdered 17 people, including election officials.

Senior intelligence officials have found a disturbing pattern to attacks against the police, especially in Chhattisgarh and Jharkhand.

'Whenever police pickets have been targeted like this incident where they (rebels) killed two policemen at Madanwada in Rajnandgaon, more ambush attacks invariably follow,' a senior intelligence official told IANS on condition of anonymity.

While rushing in reinforcements to thickly forested areas, police personnel seem to ignore the fact that vast tracts of the terrain are heavily booby-trapped with Improvised Explosive Devices (IEDs).