Punjab Chief Minister Amrinder Singh said that one of the two accused had been arrested in connection with the grenade attack on a Nirankari sect congregation in Amritsar, claiming the ISI was behind the "terror attack". "The person who is the mastermind is Inter-Services Intelligence. These (Harmeet Singh \u2018PhD\u2019 alias Happy) are only touts which they were using," news agency ANI quoted him saying. Identified as Bikramjit Singh (26), he is one of the two persons who allegedly carried out the attack at Nirankari Mission congregation. The police have also identified another accused in the case but he is yet to be nabbed. Announcing the breakthrough at a press conference, Punjab CM said, "I'm happy to announce that police nabbed one of the two persons involved. 26-year-old Bikramjit Singh has been arrested. The other man will also be arrested soon. His name is Avtar Singh." Read | Amritsar blast Updates: Can\u2019t rule out Khalistani terror group involvement, says CM Amarinder Singh Denying any communal angle in the blast case, Singh termed it a "pure case of terrorism". "Pakistan's Inter-Services Intelligence is quite active in fomenting trouble in Punjab and the grenade attack in Amritsar was a pure act of terrorism," he asserted. The grenade used in the blast was Pakistan made, the CM observed. "This is the type of grenade which has been taken from other modules. This is the one being used against forces in Kashmir and this is the one that burst. This one is made under license by Pakistan ordinance factory and is filled with pellets," Singh claimed. The chief minister also showed pictures of the two accused and assured that the second person would be soon arrested. Two men, who had their faces covered \u2014 one had a beard \u2014 forced their way into the Nirankari Bhavan by waving a pistol on Sunday afternoon. Three people including a preacher were killed and over 20 injured when two-motorcycle borne men threw a grenade on a religious congregation on the outskirts of Amritsar on Sunday. The police are handling the incident as a \u201cterrorist act\u201d. The incident had taken place inside the Nirankari Bhawan's prayer hall at Adliwal village near Amritsar's Rajasansi.