Two foreigners and four Afghans were wounded. A coalition spokesman did not give the nationalities of the injured soldiers.
AP quoted Ali Shah Paktaiwal, head of criminal investigations in the city, as saying the attacker rammed a vehicle into two four-wheel-drive Landcruisers traveling on a main road leading out of Kabul.
At least one of the vehicles was badly damaged, the agency quoted witnesses as saying.
Also today, a roadside bomb killed two Afghan security guards supervising a NATO supply convoy in southern Kandahar Province.
Provincial police commander Sayed Aqa Saqib told news agencies that three additional guards were injured in the blast, which struck their vehicle on a road in the district of Zahiri.
Elsewhere, fighting between Afghan soldiers and Taliban militants left at least eight insurgents and one police officer dead.
Probe Into 'Friendly Fire' Deaths
On August 24, the State Department said the United States will conduct a thorough investigation with Britain into the circumstances under which three British soldiers were killed in a "friendly fire" incident in southern Afghanistan.
The British military said the soldiers were believed to have been killed by a bomb dropped by a U.S. aircraft called in to help the troops fighting with Taliban insurgents on August 23.
Britain and the NATO-led International Security Assistance Force (ISAF) are also investigating.
Border Region Seizures
Meanwhile, in Pakistan, a group of pro-Taliban militants in northwest Pakistan have kidnapped a government official, an army officer, and two guards.
AP reported that the four men were seized late on August 24 in Ladha, a town in the South Waziristan tribal region bordering Afghanistan.
The Pakistani military says it is investigating the incident but has no information about the whereabouts of the kidnapped men.
(AP, Reuters, AFP)