Twenty people were tortured and murdered with clubs and knives at a Pakistan Sufi shrine, police said on Sunday, with the shrine's custodian and five associates placed under arrest.
Another three people, including two women, were critically injured during the attack at a shrine in Sargodha, in the Punjab.
The custodian and spiritual leader of the shrine, Abdul Waheed, called on the worshippers to visit the shrine and then attacked them with his accomplices, said Liaqat Ali Chattha, deputy commissioner for the area.
"As they kept arriving, they were torturing and murdering them," Mr Chattha said.
Police sources said they believed the killings started on Friday night but were not reported until Sunday when an injured woman managed to flee the scene and went to hospital.
The victims were first drugged and then killed with machetes and batons.
Zulfiqar Hameed, a regional police chief, said the custodian told police he believed his victims were out to kill him.
“The suspect appears to be paranoid and psychotic, or it could be related to rivalry for the control of shrine,” he said, adding that the investigation was continuing.
With its ancient hypnotic rituals, Sufism is a mystical form of Islam that has been practised in Pakistan for centuries.
But in recent months, Sufi shrines have been targeted by extremist Sunni militants, who consider Sufi followers to be heretics, including a suicide bombing by Islamic State of Iraq and the Levant (Isil) that killed more than 80 worshippers at a shrine in Lal Shahbaz Qalandar in southern Sindh province.
Last November, an explosion ripped through another Sufi shrine, the Shah Noorani in southwestern Pakistan, killing at least 52 people. Isil also claimed responsibility for that attack.