Germany's foreign intelligence agency eavesdropped on U.S. Secretary of State John Kerry and his predecessor Hillary Clinton, the BBC reported on Saturday, citing German media.
The Der Spiegel magazine said the calls were collected accidentally and the recordings were destroyed immediately.
Kerry has reportedly spoken to his German counterpart, Frank-Walter Steinmeier, about the claims.
Correspondents said the reports will embarrass Germany after a row about the U.S> spying on Chancellor Angela Merkel.
Merkel reacted furiously towards the end of 2013 to revelations that the National Security Agency had been listening in on her mobile, telling President Barack Obama in October that this would be a "breach of trust" between two allies.
Media reports of American snooping based on documents leaked by fugitive intelligence contractor Edward Snowden have damaged U.S. relations with key allies and were a political and personal embarrassment for Obama.
Der Spiegel said the German intelligence agency had tapped a satellite phone call Kerry made in 2013.
Reports in German daily newspaper Suddeutsche Zeitung and public broadcasters NDR and WDR said documents passed to the CIA show German spies had also eavesdropped on Hillary Clinton when she was Secretary of State.
German government sources told the newspaper and two broadcasters that they intercepted the call by chance, and she had not been deliberately targeted. They also said it happened just once.
But media reports said it had not been an isolated case.
A spokesman for the American embassy in Berlin declined to comment on the reports.
Other leaked Snowden documents also showed that the U.S. had been monitoring the email traffic of Israeli officials, including former Prime Minister Ehud Olmert and former Defense Minister Ehud Barak.