Three persons were killed and seven injured when a Malda-bound bus fell into a canal in West Bengal's Murshidabad district on Monday, police said.Two vehicles were set on fire and several police vans and fire brigade vehicles were damaged as a mob turned violent protesting against the alleged delay in commencing the rescue operation."The accident took place at around 6 a.m. when the bus from Shikarpur in Nadia district fell into Gobra canal breaking the railing of the Nalini Buske bridge."There dead bodies were recovered and seven others were rescued," a police officer said. The injured persons were taken to hospital.The number of casualties was expected to rise as some passengers were feared trapped inside the submerged bus.Primary investigation suggests the driver had lost control of the vehicle, the police said.