Suicide bomber kills four Afghan air force officers in Kabul - police
The bomber's target was the bus, said Hashmat Stanekzai, a spokesman for Kabul's police chief.
The explosion happened in the heavily secured downtown area near Kabul University amid heightened political tensions over the disputed second round of the Afghan elections.
(Reporting by Mirwais Harooni; Writing by Katharine Houreld; Editing by Nick Macfie)