Chancellor Angela Merkel has appeared before a parliamentary committee examining alleged US surveillance in Germany and the activities of German intelligence, defending her insistence that "spying among friends" is unacceptable.
The parliamentary panel is investigating alleged eavesdropping in Germany by the US National Security Agency (NSA) and its relationship with German counterparts.
The inquiry was launched a year after former NSA contractor Edward Snowden revealed details of secret US eavesdropping programmes in 2013.
Reports later in 2013 that the NSA listened in on German government phones, including Mrs Merkel's, prompted a diplomatic spat between Berlin and Washington that for a time soured otherwise good relations with Barack Obama's administration.
Mrs Merkel declared at the time that "spying among friends" was unacceptable.
But subsequent reports indicated that Germany's own BND intelligence agency may have helped the US spy on European companies and officials.
Mrs Merkel said she first heard about the BND's alleged activities in March 2015, sticking to a line set out by other officials.
And she said her comments about spying among friends remained valid.
"My standard was that spying among friends is not acceptable, and if it happens we have to intervene," she told politicians.
Asked how she felt when she first heard of Mr Snowden's revelations, Mrs Merkel said: "I have enough experience that it was clear this was a significant matter."
She also defended Germany's failure to achieve a mutual "no-spy" agreement with the US, something that her government held out the prospect of in summer 2013, shortly before a national election.
Mrs Merkel said that on the German side, "I am convinced that there was very intensive work on it", but those efforts eventually came to nothing, she said.
The chancellor stressed the importance and difficulty of "finding the right balance between freedom and security".
