US intelligence switched to spying on senior German officials after last year's order from President Barack Obama to stop eavesdropping on Merkel, the Bild am Sonntag (BamS) newspaper said on Sunday.
"We have had the order not to miss out on any information now that we are no longer able to monitor the chancellor's communication directly," said a source described by BamS as a high-ranking employee of the National Security Agency (NSA).
The paper also said it had information that the US agency currently had 297 employees stationed in Germany who were tasked with keeping watch on 320 individuals.
Most of them were German decision-makers in the fields of politics and business.
Eavesdropping on confidant
Interior Minister de Maiziere (pictured) was watched because he was a cabinet confidante of Merkel, who often sought his advice, and because of past talk that the former defense minister was tipped for the post of NATO secretary-general, BamS said.
During one moment of alleged eavesdropping, BamS said Merkel reportedly asked de Maiziere: "What shall I think?"
A German interior ministry spokesman declined on Sunday to comment on the apparently indiscretion.
BamS said an example of firms targeted in Germany was the data concern SAP, a competitor of the US concern Oracle.
This allegation was, however, rejected by the US National Security Council spokeswoman and adviser to Obama, Caitlin Hayden.
She told BamS that the United States collected no intelligence information to give US firms competitive advantages.
For months, Berlin has pushed, so far in vain, for a "no-spy" deal with Washington.
Sensitivities high in Germany
US-German ties were jolted late last year after revelations of in Germany, including the tapping of Merkel's mobile phone.
Sensitivity over snooping is high in Germany due to experiences during the Nazi era and latterly in former communist East Germany.
ipj/rc (Reuters, AFP, dpa)