The United States may have bugged German Chancellor Angela Merkel's phone for more than 10 years, according to a news report by the German magazine Der Spiegel.
The report, released on Saturday, said that Merkel's mobile telephone had been listed by the NSA's Special Collection Service (SCS) since 2002, marked as "GE Chancellor Merkel", and was still on the list weeks before US President Barack Obama visited Berlin in June.
In an SCS document cited by the magazine, the agency said it had a "not legally registered spying branch" in the US embassy in Berlin, the exposure of which would lead to "grave damage for the relations of the United States to another government".
From there, NSA and CIA staff were tapping communication in the Berlin's government district with high-tech surveillance.
Quoting a secret document from 2010, Der Spiegel said such branches existed in about 80 locations around the world, including Paris, Madrid, Rome, Prague, Geneva and Frankfurt.
The magazine said it was not clear whether the SCS had recorded conversations or just connection data.
Germany's outrage over reports of bugging of Merkel's phone by the US National Security Agency prompted it to summon the US ambassador this week for the first time in living memory, an unprecedented post-war diplomatic rift.
German spy chiefs will travel to the United States next week to demand answers following the spy allegations.
But the magazine also reported that President Obama told the German leader he would have stopped the surveillance had he known about it.
Meanwhile, thousands of protesters marched on the Capitol Hill in Washington to protest against the US government's online surveillance programmes seen as encroaching on private life.
The protesters urged Congress to reform the legal framework supporting the National Security Agency's secretive online data gathering.
People carried signs reading: "Stop Mass Spying," "Thank you, Edward Snowden" and "Unplug Big Brother" as they gathered at the foot of the Capitol to demonstrate against the online surveillance.
The event was organised by a coalition known as "Stop Watching Us" that consists of about 100 public advocacy groups and companies, including the American Civil Liberties Union, privacy group Electronic Frontier Foundation, Occupy Wall Street NYC and the Libertarian Party.
Estimates varied on the size of the march, with organisers saying more than 2,000 attended. US Capitol Police said they do not typically provide estimates on the size of demonstrations.
The protesters handed to Congress an online petition signed by 575,000 people urging lawmakers to "reveal the full extent of the NSA's spying programmes".
"It's not just Americans being caught in this dragnet. We need to stand up for the rest of the world too," Free Press media and technology advocacy group president and chief executive Craig Aaron told the crowd.
Congress plans to hold new hearings on the surveillance programmes in the coming weeks and several bills are being drafted to amend the system.