Police have launched a manhunt following the murder of two teenage girls who were seen kissing a man in a video that went viral on social media.
The girls were killed last week in the deeply conservative and war-torn northwestern area of North Waziristan in what police suspect was an act of "honour killing".
Police say the video which they believe prompted the girls' murder was shot a year ago but had only recently been uploaded on social media.
"The females were sisters, identified as Jasima Bibi and Saeeda Bibi," North Waziristan police chief Shafiullah Gandapur said.
Their family had been displaced by a military operation against militants in their hometown, he said.
He said the man who was filmed kissing them in a 44-second video was arrested on Monday together with a friend who police believe uploaded the video, but police believe the murder suspect fled to Karachi, Pakistan's largest city.
Police also said the girls' father and uncle had been arrested on suspicion of concealing the murder and evidence.
The killing is the first high-profile criminal case to be pursued in the formerly autonomous tribal region, where ultra-conservative customs present a big challenge for police.
Pakistan extended police jurisdiction to the area in 2018, ending more than a century of relatively autonomous rule in a region used by Taliban and al Qaeda militants to launch attacks in Pakistan and neighbouring Afghanistan.
Police said the girls' relatives and local residents did not want a case registered because of "local traditions", so the police became the complainant in the case.
Thousands of incidents of violence against women perceived to have "damaged" family honour are reported in Pakistan each year and many more go unreported, rights groups say.
Pakistan enacted legislation to protect against "honour killings" in 2016.
