The blast took place during morning rush hour on one of Kabul's busiest roads.
 
The force of the blast damaged about 10 cars, General Ali Shah Paktiawal, head of the police criminal investigation branch, said.
 
The wounded were taken to different hospitals in the city, he said.
 
The Taliban claimed responsibility for the attack.
 
US convoy targeted
 
Al Jazeera's correspondent Bernard Smith, speaking from the site of the blast, said the bomber appeared to have targeted a US military convoy.
 
One of the vehicles was totally destroyed but its passengers remarkably survived the blast though not without injuries, he said.

The Taliban claimed responsibility for the
Kabul suicide attack of Thursday [AFP]
Later, Lieutenant-Colonel David Johnson, a spokesman for US forces, said none of the four American soldiers travelling in a two-vehicle convoy were badly wounded.

The Kabul assault came a day after attacks on two Nato convoys elsewhere that killed five civilians and wounded four foreign soldiers.

In one incident, a suicide car bomber struck a convoy of Canadian troops in the southern city of Kandahar, killing a passer-by and wounding a soldier.
 
The Taliban claimed responsibility for the attack.
 
In the other, in neighbouring Zabul province, a roadside bomb exploded close to a vehicle carrying Romanian troops, wounding three of them.
 
Taliban killed
Meanwhile, in southern Afghanistan's violent Helmand province, US-led forces said in a statement that they had killed nearly one dozen Taliban fighters in raids on their bases.

"Nearly a dozen militants were killed and two suspected militants were detained during a coalition forces operation to degrade Taliban support networks"

US-led international forces statement
They were searching compounds in the Garmsir district on Tuesday when they came under attack, the statement said.
  
"Nearly a dozen militants were killed and two suspected militants were detained during a coalition forces operation to degrade Taliban support networks," it said.

The governor of western Nimroz province, which borders Helmand, said that 41 Taliban had been killed, including a commander named Mullah Tor Jan, as they tried to escape to Pakistan.

However, an Afghan defence ministry spokesman said he was unable to confirm the claims.
  
Separately in southern Zabul province Afghan and Nato forces attacked a suspected Taliban hideout in Daychopan district overnight, killing three "foreign" Taliban and wounding six others, Mullah Fazel Bari, the district governor, said.

UN envoy

The ongoing violence provides a bloody backdrop for a move by the UN Security Council to appoint a special envoy to Afghanistan.
 
The official will be asked to improve co-ordination between Nato forces and the Kabul government.
 
A briefing from the under-secretary general for peacekeeping said on Wednesday that the world community "sometimes has not been sufficiently united" in it's strategy for Afghanistan.

Jean-Marie Guehenno said: "The UN bears a share of the responsibility for the insufficient co-ordination for the international community.
 
"We are working to correct that."

Source: Al Jazeera and agencies