Angela Merkel has demanded answers from Barack Obama on whether the United States was bugging her mobile phone for years.
On Thursday morning the German Foreign Ministry summoned the US ambassador over the allegations.
The claims, which threaten to undermine the relationship between the two premiers, will be discussed at an EU summit in Brussels on Thursday.
And Merkel will not have been too reassured by the White House response, that her calls had not been monitored, and would not be in the future.
Merkel rang Obama to demand answers
This clearly leaves open the possibility of the Chancellor's phone being tapped in the past.
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In response, the German Bild tabloid carried a picture of Obama greeting Merkel with the US President given a huge right ear, echoing anger in the country's media.
And MEPs were not impressed:
French President Francois Hollande wants the furore over the NSA spying revelations to be put on the agenda for the meeting, following claims about US spying on French citizens.
Merkel's spokesman said she "views such practices... as completely unacceptable", the BBC reported, and demanded an "immediate and comprehensive explanation".