Four Iraqis were killed and eight others injured in the explosion of a bomb planted in the bus they were riding in Baghdad, said an Iraqi police source. In a statement, the source said the blast took place at a bus stop serving passengers heading from the Plane Yard to Baghdad. However, eyewitnesses said the blast was a suicide-bombing carried out by a terrorist who blew himself up among the passengers. As the area was sealed by Iraqi police, ambulances transported the casualties to a medical center.In another development, the US army foiled an ambush in northern Baghdad, killed a terrorist and arrested 19 others. The army, in a release, said the terrorists were preparing to set up an ambush at one of the city's main routes. The injured terrorists were transferred to a medical center and the others were referred to interrogation. Also, a US soldier killed an Iraqi prisoner in Fallujah on Tuesday. In a press release on Friday, the army said the prisoner attacked the soldier during interrogation, which made the soldier defend himself by shooting the assailant and killing him. The soldier will be interrogated.