Three devotees were killed and several injured in a grenade attack at a prayer hall in Rajasansi village in Amritsar district on Sunday, the police said. Eyewitnesses say that two men on a motorcycle, their faces covered, threw a grenade at the Nirankari Bhawan, where a religious ceremony was on at the time and fled. The cops termed attack by terrorists. NIA team arrived at the spot to probe the attack. Punjab Chief Minister Amarinder Singh held a meeting on law and order after the grenade attack.