Thirteen American citizens and three Australian soldiers have been killed in attacks in Afghanistan.
The Australians died when a man in Afghan army uniform turned his gun on them during a routine morning parade in Kandahar province.
About the same time, a suicide bomber set off a device in Kabul targeting a bus carrying American soldiers.
The massive explosion was heard across the capital.
Five International Security Assistance Force soldiers and eight civilian staff, all from the United States, were killed.
The suicide attack also killed at least three Afghan civilians and a police officer, the BBC reports.
The Taliban has claimed responsibility.
A BBC correspondent says the bombing is one of the worst ground attacks against foreign troops in Afghanistan since 2001.
The Australians who died in the Kandahar attack were involved in mentoring Afghan forces in the south of the country, according to the ABC.
An Afghan interpreter was also killed and the attacker was shot dead at the scene.