The guerrillas, who were in hiding, opened indiscriminate fire when the members of the Central Reserve Police Force 74th Battalion reached a forested area in Kala Pathar near Chintagufa around 1.30pm.
A police officer said the troopers, who formed a 99-member Road Opening Party, were readying for lunch when they came under a volley of gun fire. The Maoists also hurled hand grenades.
Eleven men were killed instantly and another critically wounded trooper succumbed to his injuries in a Raipur hospital.
The ambush triggered a major gun battle between the Maoists and the CRPF.
The six troopers who were wounded and have been warded in hospitals include Assistant Sub-Inspector R.P. Hembram and Constables Swaroop Kumar, Mohinder Singh, Jitendra Kumar, Sher Mohammed and Latoo Oraon.
Oraon is in critical condition while the others were said to be out of danger.
“The injured were evacuated by helicopter,” CRPF Deputy Inspector General M. Dinakaran told IANS.