Peacekeepers opened fire on another vehicle after it traveled at high speed toward the scene of the initial attacks and failed to stop. Two people inside the car were killed and another ran away, said a local police commander, Pashtun, who uses only one name.
It was not clear if it had been an attempted third bombing. Security forces cordoned off the area and allowed no one to approach the vehicle fearing it may explode.
The two bombings occurred within 90 minutes of each other on a 500-yard stretch of road near the headquarters of organizers of last September's legislative elections.
No casualties were immediately reported from the second blast. An Associated Press photographer saw a jeep from the International Security Assistance Force on fire. Police at the scene said a car rammed into the ISAF vehicle before it exploded.
At the site of the first bombing, the body of the slain soldier was lying under a Mercedes four-wheel-drive military vehicle that bore the brunt of the blast. Troops carried one of the wounded soldiers on a stretcher to an ambulance.
Bits of the Toyota Corolla sedan that the attacker used were strewn across the road.
Pashtun said one German soldier was killed and two others wounded. He said two Afghan police and four civilians also were wounded.
ISAF spokesman Capt. Michele Chortese confirmed the car bombing and said "some casualties" occurred. He said wounded ISAF soldiers had been taken to hospital.
ISAF has about 12,000 soldiers from 36 nations in Afghanistan and is responsible for security in Kabul as well as northern and western regions. A separate 20,000-strong U.S.-led coalition is in volatile eastern and southern parts.
Violence has increased recently as Taliban-led rebels have stepped up attacks to undermine President Hamid Karzai's U.S.-backed government. Almost 1,500 people have been killed this year, the deadliest since the Taliban's ouster in 2001.
Militants have used seven suicide bombings in the past two months. The deadliest was outside an army training center in Kabul and killed nine people.