Holbrooke, who is the US special envoy to Afghanistan and former ambassador to Germany, told weekly newspaper Die Zeit the United States and its allies had to ensure their military engagement was successful in Afghanistan.
"This is in Germany's interest as much as ours," he said, emphasising that America was determined not to let Afghanistan become a breeding ground for terrorism again. "But will the Germans honour this common interest?"
Defence Minister Karl-Theodor zu Guttenberg vowed on Wednesday Germany would decide by the end of the month whether to send more troops to Afghanistan, but he also warned the eventual outcome was likely to disappoint the United States.
Guttenberg told the Leipziger Volkszeitung daily that Germany would use the international conference on Afghanistan, due to be held in London on January 28, as the time and place to announce its plans for the war-torn country's future.
However, he stressed Germany's recommendations to allies would consist of more than just a troop commitment, and foreshadowed a smaller troop boost than the US was hoping for.
“I am not one to submit to peer pressure,” he said. I also don't need direction from the USA to form my opinion.”
He described the widely-touted figure of 2,500 extra German troops as “not realistic.”
Germany now has about 4,500 combat troops stationed in Afghanistan and is under considerable pressure from the US and other NATO allies to lift that figure substantially.
US President Barack Obama has pledged to send an extra 30,000 troops to Afghanistan, and wants the other NATO countries to share more of the burden in tackling the Taliban insurgency, which shows no sign of abating.
With more than 70,000 troops already in the country, the US leads the western forces in their fight against the Taliban.
Guttenberg also emphasised that Germany's position remained skewed towards putting greater effort into reconstruction and training Afghan police and army troops to eventually take over the security of the country.
“Our policy states: A secure future for Afghanistan is not to be achieved by military means alone. The insulated call for more combat troops does not fit with Germany's engagement so far,” he told the paper. “Of course our troops are fighting as well. But we favour more and better training of (Afghan) security forces.”
Also on Wednesday, the Rheinische Post daily reported that Chancellor Angela Merkel had set up a special cabinet committee to devise a coherent position to take to London.
The committee would include Merkel, Guttenberg, Foreign Minister Guido Westerwelle, Development Minister Dirk Niebel, Interior Minister Thomas de Maizière and Merkel's chief of staff, Ronald Pofalla.
Senior government figures have sent mixed messages lately, with Westerwelle expressing clear scepticism about any troop boost and even threatening to boycott the London conference if it focussed solely on troop numbers without considering other options such as civilian reconstruction and political development.