German politicians have reacted angrily to news of a possible US spy in the defence ministry, coming just days after the arrest of a German foreign intelligence agency worker as a suspected CIA informant.
After the federal prosecutors said authorities had conducted searches in connection with a second spying case, Chancellor Angela Merkel's coalition partners said Washington should remove any US embassy staff involved and cease spying on its ally.
Security sources told the Reuters news agency on Wednesday that the latest suspect to face investigation was from the military and worked in the Defence Ministry in Berlin, but no arrest appeared to have been made.
Other sources close to the investigation said the suspect was a German Foreign Ministry official on assignment at the Defence Ministry.
The Defence Ministry confirmed its premises had been searched but gave no other details.
"It is not yet clear what is behind this," Defence Minister Ursula von der Leyen told the Berliner Zeitung newspaper, in an excerpt of Thursday's edition.
Al Jazeera's Nick Spicer, reporting from Berlin, said: "It is probably safe to assume the member of the armed forces is of a high enough rank to have access to information that could be of interest to the Americans if it is proved the Americans have been trying to use him as a spy.
"The news comes a week after a double agent was identified as a spy within Germany's intelligence agency who had collected over 200 documents and given them to the CIA in exchange for over $30,000.
"Some of the documents were about a parliamentary committee looking precisely at the question of US surveillance on German citizens and the tapping of Angela Merkel's mobile phone."
Merkel faces political fallout for not criticising US President Barack Obama sufficiently for alleged surveillance in Germany by the US National Security Agency (NSA), which targeted her mobile phone for eavesdropping.
The new cases put further pressure on the chancellor to react.
Yasmin Fahimi, general secretary of the Social Democratic Party (SPD), who share power with Merkel's conservatives, urged the "immediate removal of embassy staff involved and the immediate cessation of all other espionage in our country".
Von der Leyen, the defence minister who is from Merkel's party, said the NSA case had "shaken confidence" in the US and it had to be made clear to the intelligence community that "not everything that is possible is politically acceptable".
Steffen Seibert, Merkel's spokesman, acknowledged there were "deep differences of opinion" with Washington on how to balance the need for security with civil rights, though German officials stress they are heavily reliant on US intelligence.
The CIA and other US government agencies declined to comment on the cases.
However, US officials acknowledged that the CIA had been involved in recruiting the detained official as an informant, and did not dispute German media reports that his initial recruitment occurred two years ago.