The attack occurred on a main road that passes by a series of government compounds and military facilities in the Afghan capital on the way to the eastern city of Jalalabad.
"Around 1:00pm, a suicide bomber blew up a car targeting a convoy of foreign forces on the Kabul-Jalalabad road," Hashmatullah Stanikzai, spokesman for the Kabul police, said.
"Our security forces have rushed to the scene to investigate, and we don't have any information on casualties yet."
An AFP reporter said that civilian ambulances and armoured vehicles from the US-led Nato mission in Afghanistan were at the blast site, which was quickly cordoned off by police.
"Our mujahideen have detonated a car bomb attack on a convoy of foreign forces today afternoon," Taliban spokesman Zabihullah Mujahid said.
"As a result of the attack, several foreign forces were killed and a number of their vehicles were damaged."
The Taliban routinely exaggerate death tolls after attacks.
A spokesman for Nato's mission in Afghanistan, the International Security Assistance Force (ISAF), said the explosion was being investigated but gave no further details.