Sri Lanka's leader of the opposition Ranil Wickremesinghe charged that people who do not support the administration was being eliminated and said an international probe was needed.
Information minister Anura Yapa denied any government involvement in the killing.
President Mahinda Rajapaksa also issued a statement condemning the killing.
The killing came days after a studio complex of Maharahaja Television, a popular privately owned broadcaster was stormed by an armed group that arrived in a white van, sprayed it with bullets and torched its main control room.
The printing press of The Sunday Leader was also torched by an unknown group earlier.
Rights groups have condemned Thursday's killing and called on the government to punish the attackers.
"Sri Lanka has lost one of its more talented, co