The German Parliament is holding hearings into NSA spying on Germany. (Senior NSA veterans Bill Binney and Thomas Drake provided testimony).
An employee of Germany’s intelligence service has been arrested on suspicion of spying for the US, reports say.
The man is said to have been trying to gather details about a German parliamentary committee that is investigating claims of US espionage.
German authorities have asked the US ambassador for “swift clarification”.
The US National Security Agency (NSA) was last year accused of bugging the phone of Chancellor Angela Merkel as part of a huge surveillance programme.
The scale of the agency’s global spy programme was revealed in documents leaked last year by a former intelligence contractor, Edward Snowden.