Pakistani authorities have arrested two men for allegedly murdering two female family members after a video which showed them being kissed by a man was posted online, police said Sunday.

The two women were killed on Thursday in a northwestern district near the Afghan border, where women often have few rights and are subjected to strict tribal codes that limit their movement outside of the home.  

"Both men have confessed to killing them," said police official Mohammad Nawaz.

The two men -- one of whom was the father of the first victim and the other was the brother of the second, were both being held in custody pending trial.

Police said the victims were in their 20s and had appeared in a short video that was posted online that showed them being kissed by a man.  The women were later gunned down in North Waziristan's remote Garyum village and buried by family members, according to Nawaz. 

Loye Daraz, a second police official in the area also confirmed details of the incident.

Police said authorities were searching for two other suspects who were believed to have been involved in the killings.

Earlier BBC reported that the girls were said to have been shot dead by a family member earlier this week in a village on the border of the North and South Waziristan tribal districts.

The killing occurred after a short mobile video of them with a young man surfaced on social media, police said.

Police have been sent to the remote area to investigate the case, according to which the girls were killed by their cousin.

DPO South Waziristan Shaukat Ali told BBC that the police are conducting raids to arrest the culprit.

The incident is said to have taken place on Thursday afternoon at Shaam Plain Garyom, a border village of North and South Waziristan in Khyber Pakhtunkhwa, according to the police report.

It said the reason behind the killing of the two girls, both cousins, was believed to be a video, which shows a young man recording himself with three young girls in a secluded area outdoors.

It appeared the video was shot nearly a year ago and most probably went viral on social media a few weeks ago, a senior police official said.

 "At the moment, our topmost priority is to secure the life of the third girl and the man before taking any action," the officer said.

Human rights activist Gulalai Ismael said the murdered girls were very young. “The reason for the murders is said to be a video in which it can be seen that both the girls were scared and one of them was trying to avoid the camera. The girls were harassed before making of the video,” she added.

 Human Rights Watch says that violence against women and girls remains a serious problem in Pakistan.

Around a thousand Pakistan women are murdered in so-called "honour killings" each year -- in which the victim, normally a woman, is killed by a relative for bringing shame on the family.

Perpetrators have often walked free because of a legal loophole that allowed them to seek forgiveness for the crime from another family member. But the government has since passed a law that mandates life imprisonment even if the attacker escapes capital punishment through a relative's pardon.

In September a Pakistani court sentenced three men to life in prison for the murder of three women filmed enjoying themselves at a wedding in 2012.