The US and NATO officials confirmed the Thursday attack, saying, “Two US soldiers and four civilian contractors were among the dead.”
Nine Afghan civilians, including two children, were also reported to have died in the blast.
Hezb-e-Islami militant group has claimed responsibility for the attack.
The explosives-filled Toyota Corolla was blown up beside foreign military vehicles at about 08:00 (03:30 GMT), Kabul Police Chief Gen Salangi said.
The force of the blast destroyed several houses and a wide area of the city has been cordoned off. At least 35 people were injured.
Afghan President Hamid Karzai condemned the "cowardly" attack.
"Terrorists and enemies of Afghanistan's peace brutally targeted a residential area," he said in a statement.
According to the latest figures released by the website icasualties.org, 3,314 foreign soldiers have been killed in Afghanistan since the US-led war began in October 2001.
The number of casualties among foreign troops peaks at this time of year, known as the Taliban spring offensive, as the militants step up their attacks on US-led forces during this period.