BERLIN - German spy chiefs will travel to the United States next week to demand answers following allegations that US intelligence has been tapping Chancellor Angela Merkel's mobile phone, as a row over US snooping threatened to hurt transatlantic ties.
Documents leaked by former US intelligence contractor Edward Snowden showing sweeping US surveillance on ordinary citizens' Internet searches and telephone records have already sparked outrage worldwide.
But the furore has intensified after allegations that world leaders including the presidents of Brazil and Mexico have been among spying targets.
This week, the scandal widened to Europe, with allegations that Merkel's phone was being tapped, prompting Berlin to summon the US ambassador -- a highly unusual move between the close allies.
"High-ranking government representatives will go rapidly to the United States in order to push forward discussions with the White House and the NSA (National Security Agency) on the allegations raised recently," Georg Streiter, the chancellor's deputy spokesman, said Friday.
German media quoting sources close to the intelligence service reported Saturday that the delegation will include top officials from the German secret service.
Merkel telephoned US President Barack Obama on Wednesday saying that such spying would be a "breach of trust" between international partners.
"Spying between friends, that's just not done," Merkel said, as she was heading into a EU summit earlier this week.
In the latest Snowden revelations, German weekly Der Spiegel reported late on Saturday that leaked NSA documents showed Merkel's phone has appeared on a list of spying targets since 2002, and was still under surveillance several weeks before Obama visited Berlin in June.
The spying row has prompted European leaders to demand a new deal with Washington on intelligence gathering that would maintain an essential alliance while keeping the fight against terrorism on track.
The 28 leaders also warn that while the bloc and the United States share a "close relationship", it must "be based on respect and trust".
A lack of trust "could prejudice the necessary cooperation in the field of intelligence gathering," they said in a statement at the close of this week's summit.
Germany and Brazil are also working on a UN General Assembly resolution to highlight international anger at US data snooping in other countries, diplomats said Friday.
The resolution would not mention the United States but would call for extending the International Covenant on Civil and Political Rights to Internet activities.
"The aim is to send a message to those who abuse the system," said a UN diplomat involved in the talks.
The Bavarian daily Suddeutsche Zeitung meanwhile suggested that France had an ambiguous role in international surveillance, having signed an accord with the "Five Eyes" grouping of Australia, Britain, Canada, New Zealand and the United States whose members share virtually all intelligence -- and have pledged not to spy on one another.
'The most serious intelligence leak in US history'
Some warn that Snowden's leaks went beyond hurting ties to hindering the fight against terrorism.
British Prime Minister David Cameron said the publication of the Snowden files "is frankly signalling to people who mean to do us harm how to evade and avoid" detection, he said, citing a massacre in a Kenyan mall in which at least 67 people died.
"It is going to make our world more dangerous," Cameron said.
Michael Morrell, who served as deputy director and acting director of the CIA, told CBS television's "60 Minutes" program that the former intelligence contractor's disclosures have damaged efforts to track possible terror threats.
"What Edward Snowden did has put Americans at greater risk because terrorists learn from leaks, and they will be more careful, and we will not get the intelligence we would have gotten otherwise," said Morrell, who recently stepped down after 33 years at the CIA.
Snowden has portrayed himself as a whistleblower concerned about NSA eavesdropping and other secret surveillance, but Morrell said the former contractor was a traitor to his country.
"I think this is the most serious leak -- the most serious compromise of classified information in the history of the US intelligence community," he said.