Relatives of victims of an arson assault mourn following the attack in Ballabhgarh.

Reuters/Ballabhgarh, India

Police in northern India have arrested four men over allegations that they burnt alive two low-caste children, an official said on Wednesday, a case that triggered a street protest and drew condemnation from an opposition leader.

Authorities ruled out caste violence as a motive for the crime but India has a long history of such incidents, and the attack will feed concerns over rising intolerance after the rumour-fuelled killing of a Muslim man by a Hindu mob recently.  

On Wednesday, two men carried the bodies of the dead children wrapped in white shrouds during a protest by about 1,000 people who blocked a major highway to the northern city of Agra, home to the Taj Mahal monument, and argued with police.

Police in the northern state of Haryana said a group of men killed the children, a girl of 8 months and her two-year-old brother, by setting alight gasoline poured through the windows of their home in Ballabhgarh district, about 50 km from the capital, New Delhi.

The parents, who hail from the bottom rungs of India's millennia-old social hierarchy rooted in the Hindu religion, were also injured in the attack, a state police official said.

The incident was a family feud and not related to caste violence, however, said Jawahar Yadav, an official from the office of Harayana's chief minister.

"This is a fight among families, not about castes. It is an unfortunate incident," Yadav told television channel CNN-IBN.

The family has alleged it was attacked by men belonging to a higher caste, in revenge for separate killings a year ago, the state police officer said, asking not to be named because he was not authorised to discuss the case with the media.

Family members could not immediately be reached for comment.

Indian Home Minister Rajnath Singh has asked the state government for a report on the incident.

Rahul Gandhi, leader of the opposition Congress party, visited the district and criticised federal and state officials for not making better efforts to protect poor people.

Caste-related violence has gripped India for decades.

In August, clashes erupted in Prime Minister Narendra Modi's western home state of Gujarat after police arrested a young leader of the influential Patel clan who organised a rally to demand more government jobs for his community.