A Pakistani official says a serial killer may have been behind the rape and murder of young girl whose killing sparked deadly clashes between protesters and police.

Rana Sanaullah, the home minister for Punjab province, says DNA testing has linked the killing to at least five other cases of child abuse and murder in the city of Kasur. Police have detained eight suspects, including two relatives of the girl.

Eight-year-old Zainab Ansari went missing last week while heading to a nearby home for religious studies. The discovery of her body, which was found in a garbage bin, ignited clashes between residents and police that killed two people and wounded three others.

The residents say the authorities were slow to respond to the girl's disappearance, charges denied by police.

Zainab's body was discovered some 2km away from her home by passers-by on Tuesday, 9 January, five days after she was kidnapped on 4 January.

People's anger turned ugly after a CCTV footage surfaced online showing the last moments of Zainab life as she is being led by a man, who is believed to have raped her and dumped her body on a pile of rubbish.

The girl was on her way to a Quran recital when a man approached her, grabbed her by the hand and led her away.

Zainab's father Ameen Ansari has said that he will "not bury Zainab until the killer is caught".

"I have nothing to say, I just want justice for my daughter," her mother was quoted as saying.

Several celebrities in Pakistan, including former cricket sensation Imran Khan, have called on the police to arrest the suspect quickly. A hashtag #JusticeforZainab has also started trending on social media.

Local media reports say that police suspect that the man who raped and murdered Zainab is the same person who abducted, raped and murdered five other children in the city of Kasur in 2017.