A blast on a passenger bus killed at least one person in the Armenian capital of Yerevan on Monday, the Armenian Emergencies Ministry said.Nikolai Grigoryan, deputy director of the ministry's rescue service, said the blast had killed one person and injured six more in a residential area near the city centre."Police have launched an investigation, but at this point it is premature to speak of the explosion's possible causes," Grigorian said.The cause of the explosion is unknown, he added.