Punjab Chief Minister Amarinder Singh suspected on Sunday Pakistan's ISI-backed Khalistani or Kashmiri militants' role in the Amritsar terror attack that killed three persons and injured twenty others, and vowed that he would not let the "forces of terror" destroy the State's "hard-earned peace".

"The possibility of involvement of ISI-backed Khalistani or Kashmiri terror groups could not be ruled out (in the Amritsar terror attack)," said Amarinder Singh in an official statement, adding the forensic teams have been rushed to the spot and "all angles were being investigated".

The Chief Minister said his Government was "on the top of things" and would "get to the bottom of the incident" soon and ensure that the culprits are nabbed and brought to book.

"Nobody will be allowed to get away with trying to disturb the peace and harmony of the state," he said.

Three persons were killed and at least twenty others were injured when two motorcycle-borne miscreants hurled a grenade at a religious congregation of over 200 devotees inside a Nirankari Bhawan at Adliwal village near Amritsar's Rajasansi area on Sunday, the police said earlier.

In his statement, the chief minister said the preliminary investigations have revealed that two men - one of them with a flowing beard and both with their faces covered - forced their entry into the hall, brandishing a pistol.

They detained the sewadar, lobbed the grenade into the prayer room and fled on a motorcycle on which they had come, he added.