A former firebrand leader of the Communist Party of India-Marxist (CPI-M) was hacked to death in Kerala, triggering a war of words between the ruling coalition and the Marxists.
T.P. Chandrasekharan, 51, was killed in Onchiyam near here on Friday night while returning home on a two-wheeler.
Police said he was attacked with a bomb and then killed. His face was badly disfigured.
The Congress on Saturday blamed the CPI-M for the murder.
The Congress-led United Democratic Front (UDF) has called for a 12-hour statewide shutdown on Saturday but said vehicles will be allowed to ply.
Left Democratic Front (LDF) convenor Vaikom Viswam denied the CPI-M's hand in the killing.
"This is (meant) to malign our party," he said. "We demand an impartial inquiry."
Chandrasekharan had left the CPI-M in 2008. In the 2009 local bodies polls, he led his newly formed Revolutionary Marxist Party to victory in his home Panchayat in Onchiyam and also in the nearby villages.
Home Minister T. Radhakrishnan has ordered a probe. Without naming anyone, he said it was known who was behind the murder.
Chandrasekharan's body is now at the Kozhikode Medical College hospital.
Chandrasekharan was close to former chief minister V.S. Achuthanandan, who now heads the opposition in the assembly.
Kerala Chief Minister Oommen Chandy is reportedly on his way back from New Delhi in the wake of the incident.
"There are leads on what has happened. We will wait for the investigation to be completed. This is a gruesome incident," said Chandy.
The Chief Minister said Chandrasekharan had told him earlier that he was being threatened by CPI-M workers.
Director General of Police Jacob Punnoose told the media in New Delhi: "As of now it looks like a pre-planned attack. A special police team has been formed to investigate it."