KABUL, Afghanistan -- An explosives-packed taxi rammed a bus carrying German peacekeepers Saturday, setting off a thunderous blast that killed four soldiers and wounded 29 others in the first deadly suicide attack against international peacekeepers in Afghanistan.
The 33 peacekeepers, after months on duty in the war-battered capital, were en route to the Kabul airport for a flight home to Germany when the blast went off, according to a spokesman for the International Security Assistance Force, or ISAF. It was unclear how many people were in the taxi.
In Berlin, German Chancellor Gerhard Schroeder condemned the attack as the "cowardly and underhanded" work of terrorists.
There was no claim of responsibility, but suspicion immediately fell on remnants of Osama bin Laden's al-Qaida network, supporters of the defeated Taliban regime and rebel leader Gulbuddin Hekmatyar. All three groups are nominal allies whom authorities blame for deteriorating security across the country.
In Kabul, Afghan President Hamid Karzai expressed his condolences to the victims and pledged "full support" in hunting down the perpetrators.
Attacks have been on the upswing, particularly in the south and east, against U.S. forces hunting for Taliban and al-Qaida fighters. Lawlessness has been on the rise, with Karzai's government still unable to impose its control outside Kabul.
Still, this was the first attack to kill international peacekeepers since the 5,000-strong force was deployed in the capital in December 2001 to help maintain law and order after the Taliban were ousted in a U.S.-led war.
A district police commander in the city, Gen. Abdul Raouf Taj, quoted witnesses as saying a yellow taxi sped toward the bus, rammed into the side of it and exploded.
German chief of staff Wolfgang Schneiderhan said the taxi first tried to slide in between several vehicles in the ISAF convoy. When this didn't work, the driver pulled up alongside the bus and triggered the explosion.
Little was left of the charred taxi, and Taj said it was unclear how many people had been inside. State television reported there were two occupants.
"We found several pieces of a body and one hand still attached to the steering wheel," Taj said of the taxi, adding the driver had been wearing traditional Afghan clothes.
An ISAF spokesman, Dutch Lt. Col. Paul Kolken said the multinational force receives regular intelligence about possible terrorist strikes, but there "was no specific threat today on that road."
In April, peacekeepers said they seized five fuel trucks in Kabul rigged with explosives for suicide attacks.
German Defense Minister Peter Struck said from Berlin that the attack showed security in Afghanistan "is not sure and is not stable." He put the toll at four peacekeepers dead and 29 wounded -- seven seriously.
Taj said the taxi's license plate was found near the scene and police were trying to trace its owner.
Immediately after the early morning explosion, tense German troops from a nearby peacekeeping barracks blocked off the dusty two-lane road where the attack occurred, just east of the city.
The soldiers halted civilian traffic and kept back journalists and some Afghan security forces.
Hordes of police and ISAF vehicles, including armored personnel carriers and ambulances, rushed to the scene to pick up wounded, and a German Sikorsky helicopter landed in the middle of the road.
Before Saturday's attack, 15 peacekeepers had died on duty in Afghanistan, all in accidents. Last month, 62 Spanish peacekeepers died when their plane crashed in Turkey as they were returning home.
On May 15, two Norwegian peacekeeping troops were shot and wounded by a renegade Afghan soldier as they traveled on a road north of Kabul. Two days earlier, a British soldier was slightly wounded when an Afghan man threw a grenade at a peacekeeping base.
In March, ISAF's headquarters in downtown Kabul was hit by a rocket, but no damage or casualties occurred. Also in March, a remote control bomb wounded a Dutch peacekeeper and killed an Afghan translator.
Germany and the Netherlands, currently in joint command of the force, are due to hand over control to NATO on August 11. Some 1,800 Canadian troops will replace the German and Dutch troops who now provide the backbone of ISAF.
In Brussels, NATO spokesman Robert Pszczel said the attack "reinforces our determination to do the job the nations have asked us to do."
In Kabul, Kolken agreed.
"Our operation here is not without risk, that's why they sent soldiers to do it," Kolken said. "It just shows that ISAF's presence is still needed."