A suicide bomber killed four Afghan air force officers and wounded five on Wednesday when he detonated his explosives near a bus carrying military personnel in the capital, Kabul, police said.

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. -dawn