NEW DELHI: Five young people in northern India are believed to have been murdered by their families or partner's relatives in suspected honour killings, in three separate incidents this week, police said Saturday.

Police arrested the father and brother of a 19-year-old Hindu woman Friday on suspicion of murdering her and her 23-year-old lover, both from the lowest Dalit caste.

The relatives allegedly strangled the couple after catching them having sex at their home in Shamli district in Uttar Pradesh state, police said.

“We have arrested the father and brother of the girl. They told us they killed them because she had brought disrepute to the family,” Bhushan Verma, investigating officer in Shamli, told AFP.

“We are investigating to see if there were more relatives involved. Both were strangled to death.” It came after another Hindu couple in their 20s were Thursday found dead in nearby Saharanpur district, also in Uttar Pradesh, after their families allegedly objected to their relationship.

Police have not ruled out suicide after the couple were found hanging inside the man's house.

“It could be honour killing or suicide. We are waiting for the post mortem reports to confirm the cause of death,” Pradeep Kumar Yadav, police chief of Saharanpur, told AFP.

Yadav said the couple were in a three year relationship and wanted to marry but faced resistance from both families.

Both of the deceased couples were biologically unrelated to one another.

However, in each case, the couples belonged to the same “gotra” — or kinship group — something considered incestuous by many Hindus despite the lack of biological links, and which can be a cause for such killings.

In a third case, police on Thursday found the body of a 16-year-old Muslim boy buried near an edible oil factory in neighbouring Muzaffarnagar district, after he earlier went missing from his home.

Police said the teenager was in a relationship with the niece of the factory's Hindu owner, adding her relatives strangled him to protect the “honour of the family”.

“We have arrested the girl's brother, uncle and cousin for the murder,” Deepak Kumar, police chief of Muzaffarnagar district, told AFP.

Marriages outside one's caste or religion still attract censure across India.

Honour killings — which often see couples targeted because their families or communities disapprove of their relationship — have been carried out for centuries in the country, especially in rural areas.

They are typically enacted by close relatives or village elders to protect what is seen as the family's reputation in a hereditary caste system.

United Nations statistics suggest 1,000 out of the 5,000 such murders that occur worldwide every year are in India.

India's Supreme Court ruled in 2011 that those found guilty of the killings should face the death penalty.