The experts of Rapid Action Battalion (Rab) said the powerful bomb, if exploded, could have blown up the bus and killed all the passengers.

Three street urchins by chance discovered the bomb having a detonator, a timer, and two batteries. Around half kilogram trinitrotoluene (TNT), two bicycle bearings and 50 to 60 small iron balls were used to make the bomb, the experts said.

The boys noticed a packet of sweetmeat under a Dhaka-Barisal-Jhalakathi bus at 8:15pm. The bus was scheduled to leave for Barisal at 11:00pm.

Seven-year-old Bazlul Karim, accompanied by Jasim, 4, and Akbar, 5, picked up the packet and found a food container inside. "As I opened the container, I found a black object which was ticking," Fazlul told reporters.

On suspicion, they boys took the box to on duty Traffic Sergeant Abu Naser Mohammad Zahir, who immediately buried the bomb under sand and informed police and Rab.

"If blasted, the bomb might have caused extensive damage," Rab explosive expert Sergeant Zakir told The Daily Star.

Rab members formed a cordon around the area, halting vehicular movement on the eastern side of Dhaka-Paturia Highway for about an hour.