The Pentagon reduced on Sunday the number of Americans killed in a Taliban car bomb attack the day before on a Nato convoy in Kabul from 13 to 10 after British and Canadian casualties were reported.
"There were five ISAF (International Security Assistance Force) service members killed, of which four were US," a defense official in Washington told AFP, speaking on condition of anonymity.
"Eight civilian employees were also killed, of which six were American. I cannot confirm other nationalities," the official said.
The Foreign Office in London earlier on Sunday said two British contractors were among the 13 foreigners who died alongside four Afghans in one of the bloodiest attacks of the decade-long Taliban insurgency.
Canada's military said a Canadian soldier was also among the dead.
US defense officials told AFP on Saturday that all 13 foreigners killed were American.