Three persons including a preacher were killed and over 20 injured when two-motorcycle borne men threw grenade on a religious congregation on Sunday.

The attack took place inside the Nirankari Bhawan's prayer hall at Adliwal village near Amritsar's Rajasansi, an incident which the police are treating as a 'terrorist act'.

"The grenade attack at the Nirankari Bhawan seemed to carry Pakistan's signature, with initial investigations indicating that the grenade used was similar to the ones being manufactured by the Pakistani Army Ordnance factory," Amarinder said.

The chief minister has announced a reward of Rs 50 lakh for anyone providing information on those involved in the blast that left three persons dead, officials said.

Information can be provided on the Punjab Police helpline - 181, they said, adding the identity of the informer will be kept a secret.

Amarinder flew in from Chandigarh along with his cabinet colleague and Amritsar MLA Navjot Singh Sidhu and PPCC president Sunil Jakhar to take stock of the situation.

He said the police had recovered similar HG-84 grenades from a terror module busted by the Punjab Police last month, indicating a high probability of the involvement of inimical forces from across the border.

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, said the chief minister, adding his government had taken serious note of the incident and was aggressively pursuing all angles of investigation.             

The culprits would soon be arrested, Amarinder promised, while talking to media after visiting the site of the attack.

He said the National Investigation Agency (NIA) was also helping in the investigations and certain leads had been unearthed.

A NIA team visited the blast site Sunday night along with their investigators and explosive experts and held discussions with the top brass of the Punjab Police.

Responding to a query, Amarinder said the attack could not be equated with the Nirankari conflict in 1978 as that was a religious matter and the Adliwal incident was purely a case of terrorism.

Violence between the Sant Nirankari Mission and traditional Sikhs on April 13, 1978 at Amritsar had left 13 dead, and sparked the subsequent wave of terrorism in the state.

Sunday's incident had no religious overtones, as per initial investigations, said the chief minister.

In response to a question, the CM said the state was already on high alert, with strict checking going on around landmark buildings and other vital public installations and infrastructure.

Police nakas had been set up in all districts and patrol parties were moving around in search of suspicious objects/activities, he said.

The chief minister said the district and police administration have been directed to explore the possibility of installing CCTV cameras at all strategic points.

Amarinder, who visited the hospital to meet the injured, announced jobs for the kin of those killed in the attack and Rs 50,000 each to the injured, in addition to their free treatment.

Accompanied by top police and administrative officials, the chief minister went around the site of the attack and examined the spot from where the grenade was lobbed by two men.

The men, armed with a pistol and their faces covered, had forced their way into the Bhawan after taking the civil guards hostage at gun point. They had lobbed the grenade into the prayer room, killing three and injuring 20.

Earlier, on his arrival, the chief minister was briefed by Home Secretary NS Kalsi, DGP Suresh Arora, IG Amritsar Surinder Pal Parmar and DC Amritsar Kamaldeep Sangh, who updated him on the progress of the investigations so far.