The imbroglio over the tapping of German Chancellor Angela Merkel's phone by the United States deepened Sunday, AFP reports.
The United States denied that President Barack Obama was personally informed for years of electronic surveillance against the German chancellor.
The German newspaper Bild am Sonntag newspaper quoted U.S. intelligence sources as saying that America's National Security Agency (NSA) chief General Keith Alexander had briefed Obama on the operation against Merkel in 2010.
"Obama did not halt the operation but rather let it continue," the newspaper quoted a high-ranking NSA official as saying.
On Saturday, the Der Spiegel magazine reported that leaked NSA documents showed Merkel's phone had appeared on a list of spying targets for over a decade, and was still under surveillance weeks before Obama visited Berlin in June.
But NSA spokeswoman Vanee' Vines, in Washington, flatly denied the claims.
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," Vines said, according to AFP.
"News reports claiming otherwise are not true," she added.
The allegations, derived from documents acquired from U.S. whistleblower Edward Snowden, have stoked global outrage that American spy agencies were responsible for broad snooping into the communications of several dozen world leaders and likely millions of ordinary people.
A poll for Der Spiegel found that 60 percent of Germans believe the scandal has damaged bilateral ties.
European leaders have since called for a new deal with Washington on intelligence gathering that would maintain an essential alliance while keeping the fight against terrorism on track.
Germany is to send its own spy chiefs to Washington to demand answers.
Merkel telephoned Obama on Wednesday, after reports surfaced that she had been spied upon, saying that such spying would be a "breach of trust" between international partners.
With anger simmering in Berlin, Interior Minister Hans-Peter Friedrich sharpened his tone.
"Surveillance is a crime and those responsible must be brought to justice," he told Bild, while Foreign Minister Guido Westerwelle decried the "highly damaging" spying among friends.
The Frankfurter Allgemeine Sonntagszeitung reported that Obama had told Merkel during their call that he had been unaware of any spying against her, while Spiegel said he assured her that he would have stopped the operation at once.
Merkel's office declined to comment on what Obama told her.
Responding to the reports of the monitoring of Merkel’s calls, White House spokesperson Jay Carney said that "The United States is not monitoring and will not monitor the communications of the chancellor."
The Guardian reported on Thursday, also based on a classified document provided by Snowden, that the (NSA) monitored the phone conversations of 35 world leaders after being given the numbers by an official in another U.S. government department.