The Frankfurter Allgemeine Zeitung said Chancellor Gerhard Schroeder had suggested that the issue could have consequences for future joint military missions abroad.
The claims about plutonium have sparked a new wave of concern across Europe, where many governments had already been conducting inquiries into fears that soldiers have faced an increased risk of cancer from the DU shells.
"This is a serious claim and we must take it seriously," he said.
The US charge d'affaires in Berlin, Terry Snell, was summoned to Mr Scharping's office, where a full explanation was demanded.
The Frankfurter Allgemeine Zeitung said Chancellor Gerhard Schroeder had suggested that the issue could have consequences for future joint military missions abroad.
More tests will now be carried out in Germany by the Institute for Radiation Protection in Munich.
Switzerland and Spain have added their voices to concern at the possible use of plutonium, and have instructed their teams already gathering evidence on the DU shells to check for plutonium.
In Italy, Defence Minister Sergio Mattarella said the health risks posed DU shells would be increased if plutonium had been used.
Earlier this week, the United Nations said it appeared that recycled uranium had been found in DU weapons fragments recovered from Kosovo.
The radioactivity of recycled uranium is higher than that found in DU.
And Swiss experts have said it is "highly likely" that if reprocessed uranium had been used, then plutonium would also be present.
The Swiss Federal Institute of Technology said the separation of plutonium from uranium during the reprocessing of nuclear fuel would normally leave traces.
Veterans' health claims
DU weapons were used by the US in Kosovo and Bosnia, and by American and British forces in the Gulf War.
Many veterans of both conflicts believe that DU has damaged their health, a claim rejected by the US and UK Governments and by Nato.
Last year, the US Department of Energy said initial DU test rounds had almost certainly contained recycled uranium.
It also acknowledged that "minute quantities of plutonium" might be contained in some DU stocks held at civil nuclear plants in the US.