Washington (AFP) – An attack that killed at least 173 people including 13 US service members during the chaotic Kabul airport evacuation last year was undertaken by a single suicide bomber, a Pentagon investigation concluded Friday. The investigation ruled out more than one perpetrator or anyone using firearms in the August 26 attack, which was claimed by the Islamic State group. At least 160 Afghan civilians and the 13 US troops were killed by the bombing, which came during the final days of the US military’s withdrawal after two decades of war, according to the investigation. The bomb explo…