The chief of the US spy agency NSA has not discussed the alleged bugging of German chancellor's phone with President Barack Obama, officials say.
Gen Keith Alexander never discussed alleged operations involving Chancellor Angela Merkel, an NSA spokeswoman said.
German media say the US has been tapping the chancellor's phone since 2002, and Mr Obama was told in 2010.
The row has led to one of the worst diplomatic crises between the two countries in recent years.
A report in German tabloid Bild am Sonntag claimed that Gen Alexander had told the president about the bugging himself.
An NSA source told the paper that Obama had not stopped the operation, and had wanted to know all about Mrs Merkel as "he did not trust her".
However a statement from the National Security Agency on Sunday denied the reports in Bild.
"[General] Alexander did not discuss with President Obama in 2010 an alleged foreign intelligence operation involving German Chancellor Merkel, nor has he ever discussed alleged operations involving Chancellor Merkel," NSA spokeswoman Vanee Vines said.
"News reports claiming otherwise are not true."
The statement does not make it clear whether the president was informed of the bugging operation by other means.
Mr Obama is reported to have told the German chancellor that he knew nothing of the operation when the two leaders spoke.
Germany is sending its top intelligence chiefs to Washington in the coming week to "push forward" an investigation into the spying allegations, which have caused outrage in Germany.
Der Spiegel's report, based on leaked documents, says a US listening unit was based in its Berlin embassy - and similar operations were replicated in 80 locations around the world.
Such a listening post would be illegal under German law, according to Germany's interior minister.
And the documents seen by the magazine suggest the US was aware of the sensitivities of siting listening stations in US embassies. If their existence were known, they say, there would be "severe damage for the US's relations with a foreign government".
A unit called Special Collection Services, based on the fourth floor of the US embassy in Pariser Platz in Berlin, was responsible for monitoring communications in the German capital's government quarter, including those targeting Mrs Merkel it said.
Der Spiegel says the NSA documents show Mrs Merkel's number on a list dating from 2002 - three years before she became chancellor.
This might indicate that there was extensive bugging of the phones of prominent people, says the BBC's Stephen Evans in Berlin.
The nature of the monitoring of Mrs Merkel's mobile phone is not clear from the files, Der Spiegel says.
For example, it is possible that the chancellor's conversations were recorded, or that her contacts were simply assessed.
Mrs Merkel phoned President Barack Obama when she first heard of the spying allegations on Wednesday.
The president apologised to the German chancellor, Der Spiegel reports.
Mrs Merkel - an Americophile who was awarded the US Presidential Medal of Freedom in 2011 - is said to be shocked that Washington may have engaged in the sort of spying she had to endure growing up in Communist East Germany.