New Delhi, March 14 (IANS): Home Minister Rajnath Singh on Tuesday said Left wing extremists were restless because of the attacks carried out against them by security forces, and called the Sukma attack on the CRPF a result of that frustration.

Making a statement in the Lok Sabha, Rajnath Singh condoled the death of 12 Central Reserve Police Force (CRPF) personnel and said that the nation will always remember their sacrifice.

"I express my condolences to the bereaved families. The nation is with them, the nation will remember their sacrifice," he said.

"The Left wing extremist groups are restless because of the unprecedented success of the forces against them. In 2016, forces have achieved success against the Left wing extremists in many states, specially in Chhattisgarh," the Home Minister said.

He said 135 extremists were killed, 700 were arrested and 1,198 surrendered in last year, and there was a 15 per cent drop in Left wing extremist incidents in Chhattisgarh in 2016.

He said the rates of surrender and arrests in 2016 were higher than the previous year as well. "The Left wing extremists faced major damage in 2016," he told Parliament's lower house.

"To uplift the falling morale of their cadres, they execute attacks like this one. I am confident our brave soldiers will fight them and end Left wing extremism soon," he said.

Singh added that the CRPF has been asked to carry out a probe to find whether there had been any mistake on their part.

"I want to assure the nation, their design of keeping parts of the country backward for their own selfish reasons will not be allowed to succeed," he said.

In one of the biggest Maoist attacks in the past two years, 12 CRPF personnel were killed and four injured in an ambush by the rebels in Sukma district of Chhattisgarh on Saturday.