A police spokesman said the attacker detonated his Toyota Sedan car at 11:20 am (1220 HRS IST) close to the destroyed Dar-ul-Aman palace in the southwest of the city, and the area was now blocked by Afghan and international forces.
"I can confirm a suicide attack on Dar-ul-Aman road of Kabul on a convoy of foreign forces," said Hashmat Stanikzai. Footage on private television channel Tolo showed coalition forces tending to at least one casualty on the ground while fire trucks and ambulances, sirens blaring, were on their way to the scene.
Water was being sprayed on one charred vehicle lying on its side. A spokesman for NATO's International Security Assistance Force (ISAF) said it was aware of an incident but the force could not give further details until further information had been gathered.
Siddiq Siddiqui, an interior ministry spokesman, confirmed the attack but also had no immediate information on casualties.
At around the same time in the eastern city of Asadabad in Kunar province, a female suicide bomber blew herself up outside a local branch of Afghanistan's spy agency, a spokesman for the Kunar provincial governor said.
The woman struck outside the local operations centre for the National Directorate of Security (NDS), said spokesman Wasifullah Wasifi.
"As a result of the explosion two guards of the operative directorate were wounded," he said.