The Sikh hardliner elements were detained in raids conducted by various teams of the state police at different places, including in Amritsar and Bathinda districts.

The police have not, however, officially confirmed or denied the detentions.

Punjab Director General of Police (DGP) Suresh Arora had earlier said that a "local hand" could be behind the grenade attack.

Three persons were killed and 20 injured when two motorcycle-borne youths threw a grenade at a religious congregation in Adliwal village in Rajasansi area, about 15 km from Amritsar, on Sunday.

All victims were sect followers from nearby villages who had gathered for the weekly religious meeting.

Police officials told IANS that various leads were being followed in the grenade attack case to nab the culprits.

Chief Minister Amarinder Singh on Monday said the attack seemingly carried "Pakistan's signature", with initial probe indicating the grenade used was similar to the ones being manufactured by the Pakistani Army Ordinance factory.

"Prima facie, this appears to be an act of terror by separatist forces, organised with the involvement of ISI-backed Khalistani or Kashmiri terrorist groups.

"My government has taken serious note of the incident and is aggressively pursuing all angles of investigation," he said.

He also announced Rs 50 lakh as reward for any information leading to the arrest of the assailants.

The National Investigation Agency (NIA) and forensic experts were helping in the investigations.

The Chief Minister has said Sunday's attack was a clear case of terrorism and there was no religious connection to it.