German officials launched a legal investigation and said the escalating scandal could disrupt counter-terrorism collaboration between the United States and European Union.
Chancellor Angela Merkel -- who alleged a day earlier the U.S. National Security Agency spied on her cellphone -- met with French President Francois Hollande about the diplomatic crisis a long-planned EU summit in Brussels, Belgium.
Three days earlier Hollande condemned alleged U.S. spying in France after documents leaked by former NSA contractor Edward Snowden indicated NSA spies intercepted 70.3 million digital communications inside France from Dec. 10, 2012, to Jan. 8, 2013.
German Justice Minister Sabine Leutheusser-Schnarrenberger, voicing anger in Berlin over the escalating disclosures, called for a halt to a European financial data-sharing program that targets suspected terrorists.
Other European officials attending the two-day EU summit said efforts to create a major U.S.-EU trade deal could be damaged as well.
Many said they were shocked a potent ally they considered a friend could have tapped their personal communications -- an act The Washington Post said was long considered diplomatically off-limits.
"Spying among friends -- that just does not work," Merkel told reporters in Brussels.
"The United States and Europe face common challenges," she said, "[but] trust has to be restored."
"We can't simply go back to business as usual," German Defense Minister Thomas de Maiziere, a close Merkel confidante, told Germany's ARD public TV. He suggested consequences were imminent without saying what they might be.
"We need to take measures and I can't imagine measures at the national level -- we need to take European measures," Belgian Prime Minister Elio Di Rupo told reporters.
U.S. intelligence agencies are "out of control," European Parliament President Martin Schulz said.
British Prime Minister David Cameron, whose NSA counterpart agency is also accused of spying on allies, had no public comment about the U.S. spying reports.
The flurry of activity was fueled by a report published online Thursday by The Guardian. The British newspaper published what it said was a 2006 memo indicating a U.S. official provided the NSA with 200 phone numbers tied to 35 world leaders.
The memo, sourced to Snowden, said U.S. government employees were encouraged to mine their contact books for the business and personal landline, fax and cellphone numbers of "foreign political or military leaders" and pass on the details on to the NSA.
President Barack Obama assured Merkel "the United States is not and will not monitor the chancellor's communications," White House spokesman Jay Carney said in Washington Thursday.
But for a second day, he did not answer reporter questions about whether the United States monitored Merkel in the past.
"We are not going to comment publicly on every specified, alleged intelligence activity," Carney told reporters.
"And as a matter of policy, we have made clear that the United States gathers foreign intelligence of the type gathered by all nations," he said.
"We have diplomatic relations and channels that we use in order to discuss these issues that have clearly caused some tension in our relationships with other nations around the world, and that is where we are having those discussions," Carney said
The Office of the Director of National Intelligence, meanwhile, is alerting foreign intelligence services documents detailing their secret cooperation with Washington were obtained by Snowden and could possibly be leaked, the Post reported Friday.
The material Snowden lifted deals with standard intelligence about the military capabilities of adversaries such as Iran, Russia and China, the Post said, citing government officials.
Some of the documents Snowden took refer to cooperation with countries not publicly allied with the United States, the Post said.
