A suicide bomber killed 8 American civilians at a US military base in eastern Afghanistan, while another bomb killed 4 Canadian soldiers and a journalist in the south of the country.US officials say a bomber detonated his explosive vest inside the Forward Operating Base Chapman in Khost province. The military said no US or NATO troops were killed or wounded in the blast, but few other details about the incident were released. The base is used to support reconstruction efforts and other civilian operations in Afghanistan. Khost borders Pakistan's North Waziristan tribal region, where Taliban militants and their allies launch cross-border attacks. In a separate attack, the Canadian defence ministry says 4 Canadian soldiers and a Canadian journalist were killed when their convoy hit a roadside bomb while on patrol just outside the southern city of Kandahar. The journalist was identified as 34 year old Calgary Herald reporter Michelle Lang. A Canadian civilian official was wounded in the blast.