At a press conference, former Delhi High Court Chief Justice Sachar said they were demanding a judicial enquiry into the incident as they have no faith in CBI or a magisterial inquiry.
His views were echoed by other activists like Swami Agnivesh, B D Sharma and Himanshu Kumar.
They said a delegation will soon meet President Pratibha Patil and Prime Minister Manmohan Singh.
In a major crackdown by CRPF, at least 20 Naxalites, including a woman, were killed in a fierce gunfight in the intervening night of June 28-29 in the dense jungles of Dantewada in Chhattisgarh that also left six jawans wounded.
Agnivesh alleged the encounter was a "cold-blooded murder" of innocent villagers and it reminded him of 'Jalianwala Bagh' massacre.
He said the Congress leaders in the state, including that of party MLA from Konta, Kawasi Lakma has noted that there were no Maoists present in the area.
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"Children have died, school students have died, women have died. How can they all be Naxalites?" he asked.
Agnivesh demanded that the Prime Minister should apologise to the Adivasi community and Home Minister P Chidambaram should be sacked from his post.
"Central government should take action against Raman Singh government in the state," he said.