Three others, also from Bihar, were injured, police sources said on Saturday. (Agencies)
The deceased, hailing from Bihar have been identified as Papu Kumar Singh (25), Shamsher Mantri (20) and brothers Ahot Bihari (20) and Raj Bihari (19), they said.
The militants stopped the bus coming from Siliguri in West Bengal to Shillong in Meghalaya at about 10 PM on NH-31 in Ramphalbeel area under Serfanguri police station.
The ultras asked the eight passengers to come out and then lined them up before opening fire on them from close range killing five on the spot, they said.
The extremists then asked the inter-state bus to proceed on its journey
The injured - Amol Gupta, Ramanand Ojah and Babulal Karmakar - have been admitted to Bongaingaon Civil Hospital.
District Additional Superintendent of Police S Panswar said that operations are on to nab the culprits and security measures stepped up.
He said that there were no prior inputs about such an attack.
Three others, also from Bihar, were injured, police sources said on Saturday.