"One or two Naxalites might have been there.
The killing of innocent tribals will generate more anger and hatred towards police and security forces," CPI General Secretary S Sudhakar Reddy said in a statement here.
Ten of those killed are in the age group of 15 to 28 years, including a 15-year-old girl, he said.
"The CPI demands a judicial enquiry by a sitting High Court judge," Reddy said and added that it will send a fact- finding delegation to "the places of massacres at the earliest".
Terming it as a "state sponsored massacre of civilians", CPI (ML) said, "Any attempt to dress up a heinous massacre of civilians as an encounter must be prevented."
"A judicial enquiry must be ordered into the killing without delay, and the police and CRPF personnel responsible for the incident must be booked for murder and brought to trial," it said in a statement.
At least 20 Naxalites, including a woman, were killed in a fierce overnight gunfight in the dense jungles of Dantewada in Chhattisgarh that also left six jawans wounded.
The encounter, which took place in the forests of Silger, an uncharted Maoist zone between the Naxal hotbed of Jagargunda and Basaguda in Bijapur district of Bastar region, was launched on Wednesday night in a joint operation by over 300 CRPF and state police personnel from three directions.