Four personnel were also injured in the Naxal attack and two of them were stated to be critical.
The incident occurred in the dense forests near Kottacheru village under Bhejji police station, around 450 kms away from the state capital, at 9:15 AM when 112 personnel of CRPF's 219th battalion were out for a road opening task.
The Bhejji area in south Bastar region of the state is notorious for Naxal attacks and many security personnel have been killed here in the past.
The Naxals also looted ten weapons like INSAS and AK series assault rifles and two radio sets from the killed men, officials said.
"The troops were part of the road clearing party that has been securing an under-construction road between Bhejji and Kottacheru. They were ambushed by Naxals who set off multiple hidden IEDs on the ground and opened fire. The squad effectively retaliated before twelve made the supreme sacrifice," acting CRPF DG Sudeep Lakhtakia told PTI.
He added that Maoists are trying to disrupt normal life and activities in this area as the Central Reserve Police Force has increased its presence here and got re-opened a local 'haat' (market) last year here after it was forcibly shut by the red ultras.
Prime Minister Narendra Modi took stock of the situation and spoke to Home Minister Rajnath Singh who will be travelling to Sukma.
Chhattisgarh Chief Minister Raman Singh has strongly condemned the Maoist attack and described it as a "cowardly act".
Security personnel have laid down their lives to free Bastar from violence and Maoist terror. Their sacrifice will not go in vain. "I salute their sacrifice," the CM said, adding ultras were frustrated with development of road network in the region.
He also extended condolences to the bereaved families.
The CRPF chief and senior officials are also rushing to Raipur.
A senior Chhattisgarh official told PTI that the road opening party was passing through the forests between Bhejji and Kottacheru villages when Naxals opened indiscriminate fire on them.
According to a CRPF official, summer season is regarded as an offensive period by rebels as they observe annual 'tactical counter offensive campaign' (TCOC).
The dry weather is a favourable period for carrying out ambushes in the vast jungle terrain and this attack would have been planned by Maoists led by hardcore naxal cadre Hidma who is active in southern part of Bastar, the paramilitary official added.
However, further investigation would reveal the details, he added.
The injured have been air lifted and brought to the CRPF field hospital in Bheji and few others have been transferred to Raipur.
A special counter-Naxal team of CoBRA has been rushed to the ambush spot as reinforcement to sanitise the area and launch a search.
Another senior CRPF officer said the ambush site has very weak mobile phone connectivity and communication is being done through satellite phones.
"It is estimated that a hundred plus Maoist squad was present in the area when the ambush was launched. These are preliminary inputs. More details are awaited," the officer said.
The deceased CRPF personnel have been identified as Inspector Jagjit Singh, Assistant Sub-inspectors H B Bhatt and Narender Kumar Singh, Head Constables Jagdish Prasad Vishnoi and P R Minde and Constables Mangesh Pal Pandey, Rampal Singh Yadav, Goraknath, Nand Kumar Patra, Satish Kumar Verma, K Shankar and Suresh Kumar.
Constables Jaidev Parmanik and Salim are critically injured.
The CRPF is working without a regular chief for over a week now as the government has not appointed a new Director General after K Durga Prasad retired on February 28.