The Afghan Taliban, ousted from power by a U.S.-led coalition in 2001, claimed responsibility for the attack, the latest in a wave of bombings to hit Kabul as the majority of foreign combat troops withdraw from the country by the end of the year.
A witness saw at least three bodies from the blast in a nearby hospital, but their nationalities were unclear.
Officials would not confirm any deaths on the record, though they said several bystanders were wounded.
"I can confirm it was a British vehicle and there are some injuries. We are working with the Afghan authorities," said the spokesman, who asked not to be identified.
General Ayoub Salangi, the Afghan deputy interior minister, said the bomber was riding a motorcycle.
The blast wounded 33 Afghan bystanders and destroyed three cars, Interior Ministry spokesman Sediq Sediqqi said.
Taliban spokesman Zabihullah Mujahid said in a text message that a suicide bomber "targeted foreign invading forces" and many were killed and wounded.
On Monday, a bomb in Kabul killed two U.S. soldiers as they were travelling in their vehicle.

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