The Punjab Police has formed several teams to investigate the grenade attack in Adliwal village in Rajasansi area. CCTV footage of places near the blast was being scanned to know more about the two masked attackers.

Forensic teams and a team of the National Investigation Agency (NIA) reached the spot late on Sunday to start the probe.

While some injured have been discharged from the Amritsar hospital, others are still recuperating. One of the injured was still serious, a police officer said.

Inspector General (Border Range) S.P.S. Parmar told the media on Monday that the probe would look at all angles and police teams were trying to trace the culprits.

In a major terror attack, three persons were killed and 20 injured when two motorcycle-borne youths threw a grenade at a Nirankari congregation about 15 km from Amritsar.

The attack on the campus located in the rural belt, around three kilometres from the Guru Ram Das Jee Amritsar international airport, created panic.

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

Punjab Director General of Police Suresh Arora, who immediately rushed to the spot along with senior officers, admitted that it was a "terror act".

TheAPunjab Police has drawn flak for intelligence failure regarding the attack despite the border state being on high alert since Nov 14 regarding the movement of six to seven terrorists in the state.

Eyewitnesses told the police that two youths on a motorcycle, their faces covered, forced entry to the sect campus by pointing a pistol at a woman volunteer at the gate.

There were around 200 followers in the campus at the time.

Amarinder Singh, who on Sunday directed the police to immediately enhance security arrangements at all sensitive places, terming it as "the first such indiscriminate attack on innocent people in recent past", said that the "possibility of involvement of ISI-based Khalistani/Kashmiri terror groups cannot be ruled out".

The Nirankari sect, with headquarters in Delhi, has millions of followers across the country and abroad.

In the last few months, Khalistani and Kashmiri activists have been trying to foment trouble in Punjab, which shares a 553-km long barbed wire fenced international border with Pakistan.

The Punjab Police, along with its Jammu and Kashmir counterpart, had busted two modules of Kashmiri students who were studying in institutions in Punjab and having links to terrorist outfits in troubled Kashmir.

The Maqsudan police station was targeted by Kashmiri terrorists on September 14 with hand grenades though no one was injured in the attack.

Posters of Kashmiri terrorist Zakir Mussa had mysteriously appeared in Punjab's Gurdaspur district on Friday saying that he had been seen in Punjab.

The Chief Minister said 15 terror modules had been busted in the past 18 months, including those with Kashmiri terror links.