NEW DELHI: Following a knock at his front door, an Indian scholar greeted two unidentified visitors and was shot in the head and the chest, becoming the third critic of religious superstition to be killed in the country in three years.

The attack on Malleshappa M. Kalburgi sent a chill through Indian civil society, stoking worries about religious extremism and intolerance and prompting an outpouring of condemnation as the 77-year-old author and academic was cremated Monday in his hometown of Dharwad, in the southern Indian state of Karnataka.

"This incident should not have happened. It is highly condemnable," Karnataka Chief Minister Siddaramaiah told reporters.

Authorities are searching for two men who according to Kalburgi's daughter arrived on a motorcycle at their home Sunday, knocked on the door and fired two shots that killed her father, Inspector S.S. Hiremath said. He declined to give further details about the attack.

Police are investigating whether Kalburgi's murder is connected to death threats he received last year from angry right-wing Hindu groups after he criticised idol worship and superstitious beliefs by Hindus. He was provided police security after the threats but it was removed about two weeks ago at the scholar's request, police said.

The attack was widely condemned.

"Everyone has the right to express his opinion," actor and director Girish Karnad said. "If this grows in Karnataka, we are in trouble."

Columnist Nitin Pai, who founded a think tank in the southern city of Bangalore, said on Twitter that he was "Shocked at the murder of M.M. Kalburgi. Disgusted that his killers have apologists among us."

India has long held secularism to be a keystone of its constitution — and a necessity for keeping the peace among its cacophony of cultures defined by caste, clan, tribe or religion, including Islam, Christianity, Judaism, Hinduism, Sikhism, Jainism and Buddhism.

Earlier this year, unknown attackers gunned down another anti-superstition crusader, Indian writer and communist politician Govind Pansare, as he and his wife were taking a walk in western Maharashtra state.

In another daytime attack in 2013, two assailants gunned down Narendra Dabholkar, a 68-year-old doctor-turned-activist, while he was out for a walk in the Maharashtra city of Pune, near Mumbai.

Police have arrested two suspects in Dabholkar's murder. He had received years of death threats and demands that he stop giving lectures in villages across Maharashtra state promoting rationalist thought and discouraging superstitions, religious extremism, black magic and animal or human sacrifice.

Maharashtra's government later passed long-stalled legislation that Dabholkar had worked on banning religious exploitation and fraudulent medical workers.

Activists have said the legislation does not go far enough since it only allows complaints from victims and their families, not from third parties, which they say limits the law's effectiveness because most victims are invested in superstitious beliefs and are not likely to complain.