An Anti-Terrorism Court (ATC) on Monday gave police three days to finish the interrogation of four men suspected in the killing of 20 devotees at a shrine near Sargodha on Saturday night.

The custodian of the shrine, Abdul Waheed, and his four alleged accomplices drugged the 20 men and women at a house near the shrine. The victims were then beaten with batons and repeatedly stabbed.

The motive for the slaughter remains unclear but some officials earlier said the chief suspect had mental health problems and had used violence on followers before.

The regional police chief Zulfiqar Hameed earlier told AFP, "The 50-year-old shrine custodian, Abdul Waheed, has confessed that he killed these people because he feared that they had come to kill him."

"The suspect appears to be paranoid and psychotic, or it could be related to rivalry for the control of shrine," he had said.

Police officer Shamsher Joya said the four appeared before the court on Monday where Judge Zahid Iqbal extended their custody pending the investigation.

There have been cases of people dying during exorcism ceremonies at some shrines across the country, but mass killings are rare.