Two men, a Pakistani and a Tajik, were arrested for planning the attack after their vehicle was stopped last Thursday in Auraq, a suburb near the town of Masar-i-sharif, the main base of Germany's 3,200 troops in Afghanistan. The car was packed with 220 kilogrammes (485 pounds) to 300 kilogrammes of explosives, according to the German Defence Ministry.
According to German television channel N24 the two men have confessed and have been sentenced to be hanged. Citing unnamed sources within the Afghan intelligence service, the report said the men planned the strike in connection with terror organization Al Qaida.
According to the television report, the explosives were hidden in the vehicle's doors and floor and were to be detonated by remote control.
"We have seldom experienced something this professional," the television report quoted an unnamed German officer as saying.
Germany has been under pressure from its NATO allies to deploy its troops from the relatively safe north of Afghanistan to the south of the country where US, British and Canadian troops are bearing the brunt of a Taliban insurgency.
Chancellor Angela Merkel's government maintains that sending German troops to the south would jeopardize their reconstruction work in the north.
The German army's chief of staff, Wolfgang Schneiderhan, was quoted as saying in April he was worried about an increase in violence in the north in the wake of a string of attacks on German troops and their Afghan helpers.
Twenty-six German troops have died in Afghanistan since 2002.
In late March an explosion seriously injured two German soldiers near Kunduz in northern Afghanistan. Ten to 15 kilogrammes of explosives were used in that attack.
In late February militants fired five missiles at the Germans' barracks in Kunduz. The German troops are part of the 47,000-strong NATO-led International Security Assistance Force in Afghanistan.