It was the deadliest day this year for Western troops in Afghanistan, The New York Times reported.
Meanwhile, Afghan intelligence prevented an attack by militants in Kabul, the Afghan Khaama Press reported.
The militants were planning a missile attack in Kabul but Afghan forces, in cooperation with local residents, foiled it and seized about 30 75mm artillery rounds and 20 82mm artillery rounds, the National Directorate of Security said in a statement.
Capt. Dan Einert, a spokesman for the international coalition, said the five killed in a roadside bomb attack in the Maiwand district in Kandahar province were Americans, the Times said.
The nationalities of two soldiers fatally shot in an insider attack in Farah province in western Afghanistan and one who died in a small-arms attack in northern Afghanistan had not been released, the newspaper said.
The Taliban claimed responsibility for the insider attack, in which an Afghan National Army soldier turned his weapon on his trainers after an argument.