A car bomb has killed four German peacekeepers and injured dozens of other people in an apparent suicide attack on a bus in the Afghan capital, Kabul.
A helicopter landed to provide medical assistance
The force of the explosion threw the vehicle off the road, a few kilometres east of the city centre, near a base used by German and Dutch troops of the International Security Assistance Force (Isaf).
The attack is the deadliest assault on the Isaf force since it arrived in Afghanistan to support the government of Hamid Karzai after the removal of the Taleban.
German Defence Minister Peter Struck said the attack had "a new and horrible dimension" but it would not lead to Germany's withdrawal from the international force it leads jointly with the Netherlands.
US military sources said the attack was carried out by a suicide bomber, who drove a taxi filled with explosives towards the bus, then blew it up.
The soldiers were being driven to the airport to fly home to Germany after a six-month tour of duty in Afghanistan.
The other 29 peacekeepers on board the bus were injured, at least seven seriously, as were several Afghan civilians who were near the scene of the blast.
Isaf has UN mandate to help Afghan Transitional Authority maintain security
Aims to develop reliable security structures, identify reconstruction needs and train Afghan security forces
Comprises 4,600 troops from 29 nations, currently led by Germany and the Netherlands
Area of responsibility limited to Kabul and vicinity
Commander is Lt General Norbert van Heyst of the German Army
An Isaf spokesman said an investigation had been launched into the cause of the blast in close co-operation with the Afghan authorities.
The BBC's Kylie Morris in Kabul says the road where the explosion occurred is busy and lined with stalls. Some of the casualties are thought to have been seriously wounded.
The area was quickly blocked off and a German military helicopter landed on the road to give medical assistance.
The injured were then taken to military hospitals.
President Hamid Karzai offered his
condolences and said the peacekeepers had given their lives for the Afghan people.
German Chancellor Gerhard Schroeder condemned the attack as the "cowardly and devious" work of terrorists.
Mr Schroeder received condolences from US President George W Bush and the two men agreed that "the fight against terrorism is not over and both Germany and America have a special responsibility in Afghanistan to help make it a stable democracy and not a base for terrorism," Defence Minister Struck said.
"We have been doing everything possible to protect them but one can never rule out a suicide attacker," Mr Struck said.
"We will carry on with our assignment, making a contribution to stabilising the area," he said.
About 5,000 international peacekeepers have been deployed to patrol the streets of Kabul and to provide security for the capital.
Our correspondent says it is too early to say who was responsible for the blast, but local Afghan officials have blamed the attack on remnants of al-Qaeda or Taleban.
German soldiers are part of the Kabul peacekeeping force
Anti-government forces have been issuing pamphlets calling on Afghans to rid their country of the peacekeeping forces, our correspondent adds.
Suspected Taleban fighters have been stepping up attacks in recent weeks, particularly in the south and east of Afghanistan.
About 40 Taleban fighters were killed recently in the south of the country in a battle with Afghan government forces.
Saturday's explosion was the second violent incident involving German peacekeepers in Kabul in recent weeks.
On 29 May, a German soldier was killed and another wounded when their vehicle hit a landmine near Kabul.
And last month more than 60 Spanish peacekeepers were killed when a plane that was flying them home from their mission in Afghanistan crashed.