Nato troops have killed a civilian at the scene of a suicide bomb attack in Kabul, Afghan and Nato officials say.

Several others were injured when the US soldiers opened fire. The US military said the shooting had been accidental.

At least three people died in the suicide bombing, officials say. Another civilian died in a suicide bombing later on Saturday in Mazar-e-Sharif.

Saturday's attacks bring to four the number of suicide bombings in Afghanistan in the past two days.

Suicide attacks have become a regular feature of the Taleban's campaign against the Western-backed government of President Hamid Karzai in recent years.

'Accidental discharge'

The BBC's Charles Haviland in Kabul says there is considerable confusion surrounding the shooting incident at the scene of the early morning bombing in the city.

Nato's Isaf force said two Afghans had accidentally been shot by its soldiers. One of the Afghans later died, it announced with regret.

"Initial indications are that an Isaf soldier's weapon accidentally fired," said Isaf spokesman Maj John Thomas.

The US military says it is investigating how the firing occurred.

Spokesman Col David Accetta said US soldiers had "responded" to the suicide attack but had not intended to fire on anyone.

"It appears to have been an accidental discharge," he told the AFP news agency. "There might have been a weapons malfunction or some other cause. We don't know."

Anger over civilian casualties has been growing among Afghans and crowds gathered at the scene to protest afterwards.

Convoys targeted

In the suicide attack on Kabul's western outskirts, a man drove a taxi packed with explosives at a foreign convoy, killing himself and several others.

The blast was powerful enough to shatter shop windows.

The government says an Isaf convoy was the target of the attacker, but Isaf and the US-led coalition said it appeared that private security vehicles had been targeted.

Suicide attacks have claimed hundreds of lives in Afghanistan and are on the rise.

One in southern Afghanistan on Friday killed some 10 people, including six children and a Dutch soldier.

Saturday's blast in Mazar-e-Sharif injured another 12 people, security officials in the northern city told the BBC.

They said the attacker rammed his motorbike into a passing Nato convoy. There were no reports of Nato casualties.

PHOTO CAPTION

An Afghan policeman guards the site of the Kabul bomb attack