The explosion sparked a fireball and littered the street with shrapnel and twisted metal hulks. Heavy black smoke poured from burning wreckage at the site along the four-lane highway frequently used by foreign military trainers in the southwestern section of the city.
Underscoring the difficulties ahead, the brazen assault occurred on the same day that top NATO and Afghan officials were meeting elsewhere in Kabul to discuss the second phase of shifting security responsibilities to Afghan forces in all or part of 17 of the country's 34 provinces.
It also was a blow to efforts by the U.S. and President Hamid Karzai to forge peace with the fundamentalist Taliban movement as NATO plans to withdraw all its combat troops from the country by the end of 2014, with support for the costly war reaching new lows in the West.
NATO said five coalition service members and eight civilian contractors working for the coalition died in the explosion.
A U.S. official said all were Americans, but Canadian defense spokesman, Lt. Col. Christian Lemay, told The Associated Press that a Canadian soldier was among the troopers killed.
The Afghan Ministry of Interior said three Afghan civilians and one policeman also died in the attack. Eight other Afghans, including two children, were wounded, said Kabir Amiri, head of Kabul hospitals.