Fresh allegations emerged on Monday that the US tracked 60.5 million calls in Spain in a single month even as Washington denied media reports on Sunday that President Barack Obama had the knowledge of US spy agencies monitoring German Chancellor Angela Merkel's phone calls.

The National Security Agency (NSA) spokeswoman Vanee Vines denied allegations in Germany's Bild am Sonntag newspaper that the agency's chief General Keith Alexander had briefed Obama on the tapping of Merkel's phone in 2010.

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.

"News reports claiming otherwise are not true," she said.

German media reported over the weekend that NSA tapping of Merkel's phone may have begun as early as 2002, when she was Germany's main opposition leader and three years before she became chancellor. She was still under surveillance just weeks before Obama visited Berlin in June.

The NSA stopped spying on Merkel after the White House learned of the monitoring in an internal review in August that found the NSA had tapped the phones of some 35 world leaders, The Wall Street Journal reported Monday, which was the first public acknowledgement that there was US eavesdropping.

According to The Wall Street Journal, US officials said that Obama was "briefed on and approved of broader intelligence-collection 'priorities,'" but decisions about specific intelligence targets were made by people below him because there were so many spying operations and it would have been impractical to brief him on all of them.

"These decisions are made at NSA," the journal quoted the unnamed official as saying. "The president doesn't sign off on this stuff."

"It appears to be unimaginable that the US president had no information on such major spying targets of his intelligence agencies," Li Haidong, professor of the Institute of International Relations at China Foreign Affairs University, told the Global Times.

The denial may come as an effort by the US to minimize the negative impact that the issue may exert on its relationship with Germany, Ni Feng, deputy director of the Institute of American Studies at the Chinese Academy of Social Sciences, told the Global Times.

China called on the international community on Monday to speed up the formulation of guidelines for cyberspace under the lead of the UN. Foreign ministry spokeswoman Hua Chunying said at a daily news briefing that the US has harmed other countries' sovereignty, invaded personal privacy and affected the public's trust and confidence.

Amid the deepening imbroglio over the spying, the NSA was revealed on Monday by a Spanish newspaper to have tracked 60.5 million phone calls in Spain in a single month from December 10, 2012 to January 8 this year.

 "Despite the simmering tensions, the US' spying activities will not pose essential influence on US-Europe relations. However, it may destroy Obama's efforts to improve the image of the US damaged by its previous activities like Iraq war," Ni said.

Agencies contributed to this story