Two civilian bystanders, including a child, were wounded in Monday's attack, said Parwan provincial police chief General Abdul Rahman Sayed Khail.

A district official said the attacker detonated his explosives-packed Toyota Corolla behind the convoy one kilometre outside Bagram Air Field. The convoy was heading towards Kabul.

A coalition spokesman at Bagram, which is about 50km north of Kabul, confirmed there had been a bomb blast.

Lieutenant Colonel Paul Fitzpatrick told AFP there had been no coalition casualties.

Responsibility claimed

According to AFP, the Taliban acknowledged responsibility for the attack, saying it was carried out by an Afghan wanting revenge for the death of two of his brothers in a May 29 road accident involving a US military vehicle in Kabul.

Riots broke out in May after a US
truck accident killed five Aghans

A purported Taliban spokesman, Mohammad Hanif, told AFP by satellite telephone that the man "had sworn to take his revenge from Americans since his two  brothers were killed in the American accident". 

"He became ready to take his revenge from Americans using Taliban facilities," he said.

On May 29, a US military truck from Bagram lost control after a brake failure hitting a dozen civilian cars at the northern entrance of the city. About five Afghans were killed.

The crash set off a day of rioting that was the worst since the Taliban was toppled from government in late 2001. About 20 people were killed in the unrest.

Karzai losing support

The latest incident comes as The Washington Post newspaper reports that Hamid Karzai, the Afghan president, is losing support as a Taliban-led insurgency escalates and his government fails to stem endemic corruption.

Karzai says US-led forces have
adopted the wrong approach

"The president had a window of opportunity to lead and make difficult decisions, but that window is closing fast," the newspaper cited an unidentified foreign military official as saying.

On Thursday, Karzai complained about what he called a lack of full co-operation from his foreign allies, saying US-led forces had adopted the wrong approach in Afghanistan and urged Western powers to provide more help in training and equipping the Afghan army and police.

The newspaper said Karzai had bristled at international criticism that greeted his recent naming of 13 police officials, some of whom have been accused of human rights abuses.

Political interests

Foreign officials and analysts said the appointments were intended to create ethnic and political balance and were not based on qualifications, the newspaper said.

"President Karzai is the only alternative for this country, but if he attacks us, we can't help him project his vision. And if he goes down, we all go down with him"

Unnamed foreign military official

"He's making decisions for short-term stability that go against his own interests and the long-term interests of building the country," an unnamed European official told the newspaper.

"As a result, international support for him is eroding and it could become a real rift at the worst possible time."

Several European governments are expressing concerns about Karzai's leadership, the Post reported, without singling out the countries.

"There is an awful feeling that everything is lurching downward," a Western diplomat told the newspaper.

"Nearly five years on, there is no rule of law, no accountability."

Aid workers freed

Also on Monday, five Afghan aid workers, including three employed by a Swedish agency, were released after four days in captivity, a police official said.

The five - two doctors and an employee of the aid agency Swedish Committee for Afghanistan and two local government workers - were kidnapped on Thursday while driving in the eastern Nuristan province, said deputy provincial police chief Ghalamullah Nuristani.

Their abductors released them late on Sunday after efforts by police and tribal elders, said Mohammed Asel Totakhil, the province's police chief.

No details were released on the kidnappers.

The five had travelled to inaugurate a health clinic in a remote village and on the return trip were kidnapped in a mountainous area in the Kamdesh district, Nuristani said.

The Swedish Committee for Afghanistan had no immediate comment.

Coalition soldier dies

In eastern Afghanistan, a coalition soldier died from injuries he sustained in combat, the US-led force said on Monday, bringing the number of coalition fatalities to seven in less than a week.

The soldier was wounded in combat on Sunday in the Peche district of the eastern province of Kunar on the Pakistani border, the military said in a statement.

The soldier's nationality was not released.

The coalition of more than 20,000 troops, most of them American, has been fighting the Taliban in southern and eastern Afghanistan for nearly five years.