The German government wants a quick and clear explanation from Washington for U.S. intelligence's apparent contact with a German man arrested last week on suspicion of being a double agent, the Interior Minister said in a newspaper interview.
"I expect everyone to cooperate promptly to clear up these allegations - with quick and clear comments from the United States as well," Thomas de Maiziere told Bild am Sonntag newspaper, according to excerpts of its Monday edition.
The White House and State Department have so far declined to comment on the arrest of a 31-year-old employee of Germany's BND foreign intelligence agency, who admits passing documents to a U.S. contact, according to intelligence and political sources.
Local media reported on Sunday that the man had been working for the CIA for around two years, the French news agency AFP reported.
The Frankfurter Allgemeine Sonntagszeitung and Bild am Sonntag said the suspect had passed on two documents about a parliamentary panel established earlier this year to investigate NSA surveillance after revelations by fugitive former intelligence contractor Edward Snowden, AFP reported.
The allegations have raised fresh tensions between the two allies.
"If reports are correct, we are not talking here about small potatoes," Foreign Minister Frank-Walter Steinmeier said in a tweet, following reports of U.S. spying that have sparked anger in Germany after revelations the NSA allegedly tapped Chancellor Angela Merkel's phone.
A parliamentary committee is looking into those allegations, revealed by Snowden.
German ties with Washington have been sorely tested by revelations last year of large-scale snooping on Germany by the U.S. National Security Agency.
Surveillance is a sensitive issue in a country where the memory of the Nazi's Gestapo secret police and communist East Germany's Stasi means the right to privacy is treasured.
'That is enough'
Head of state Joachim Gauck, a former Protestant pastor and rights campaigner in the old German Democratic Republic, told German TV the NSA affair was "a vexing episode."
"If it really is the case that a service has been using an employee from our service in this way, we have to say: 'That is enough,' " the president said in a television interview to be broadcast later on Sunday.
De Maiziere, one of the cabinet ministers closest to Merkel, called it a "very serious case" which must be investigated fully to "gauge the scale of the alleged spying and especially answer the question of who was involved."
The U.S. ambassador was called in on Friday to hear Berlin's request for an explanation and Foreign Minister Frank-Walter Steinmeier said on Sunday it was in Washington's own interests to help with the "quickest possible clarification of the facts."
It is not clear whether Merkel discussed it with President Barack Obama in their phone call on Thursday but her spokesman Steffen Seibert said: "We don't take the matter of spying for foreign intelligence agencies lightly."
One lawmaker on the committee investigating the NSA affair said the man arrested had no direct contact with the committee, whose meetings are confidential, and was "not a top agent.”
The suspect had offered his services to the United States voluntarily, intelligence and political sources said, and had been paid about 25,000 euros ($34,100) for passing on 218 BND documents to his unidentified American contact.
No-spy agreement attempted
After the Snowden revelations, Berlin demanded Washington agree to a "no-spy agreement" but the United States has been unwilling to make such a commitment. German officials also emphasize that they rely on intelligence from U.S. agencies.
The U.S. Central Intelligence Agency and the National Security Council have declined to comment.
Former Secretary of State Hillary Clinton said at a book presentation in Berlin it's “a serious issue.”
“Let's find out what the facts are and then let's act appropriately, but also try to be careful not to undermine the necessary cooperation which exists between us,” she said.
Some information for this report provided by Reuters, AFP and AP.