Alleging a "nexus" between the ruling BJP and Maoists in Chhattisgarh, the Congress on Wednesday said both are "hand in glove" to "protect" each other's interests.
The party also kept up its offensive against chief minister Raman Singh by seeking his resignation over the "failure" to protect the lives of its leaders.
Party spokesman Bhakta Charan Das said: "There is substance in our charges (of BJP-naxal nexus) and we are making them forcefully".
Meanwhile, he dismissed suggestions that the incident occurred due to collusion of some state party leaders with Maoists.
The party reiterated its charge that no proper security arrangements were made along the 'parivartan yatra' route despite prior information to the state administration.
"Is not a fact that the failure to provide security for the yatra was due to lapse of the state intelligence?" Das asked. "If this is so, why no action has been initiated against the state intelligence chief who is a trusted officer of the chief minister?"
Madhya Pradesh state Congress president Kantilal Bhuria also echoed Das's thoughts and accused Raman Singh's government of having a hand in the attack on Congress leaders in Chhattisgarh last week.
While addressing the mediapersons at Nayaa Gaon after a function, Congress president Kantilal Bhuria said the chief minister "was in the know of the attack on the Congress leaders, as he was heard giving a graphic detail of the incident to the BJP president Rajnath Singh while it was still on."
"Who was passing on all the details of the ground zero to the CM," he asked the mediapersons, adding, "How did the Maoists know that the Congress leaders on their hit list were in that convoy?"
Bhuria said the investigation into the attack would put the state government in the dock soon.
Heavily armed Maoists ambushed a convoy of Congress leaders in Chhattisgarh's Bastar region on Saturday, killing 27 people, including state Congress chief Nand Kumar Patel, senior leader and Salwa Judum founder Mahendra Karma and ex-MLA Uday Mudliyar, besides leaving 37 others injured, including former Union minister VC Shukla.