A bus that was on its way to collect school children came under petrol bomb attack on the Dadrahani Bridge at Bharatpur Metropolitan City-20 this morning, police said.Spokesman for the District Police Office Chitwan, Deputy Superintendent Bhesh Raj Rijal said some unknown assailants who came in a group of six threw petrol bomb on the bus (Bagamati Province 06001 Ka 0045) this morning.They ordered the driver and his helper to disembark before hurling the Molotov cocktail on the bus. The bus caught fire due to this and was completely burnt.”Police have initiated investigation into the incident and who threw the petrol bomb and their motive would be known only after this,” DSP Rijal said.