British officials have reportedly threatened to cease intelligence cooperation with Germany if its inquiry into British and American espionage continues.

Britain’s spy chiefs are concerned that Germany’s investigation may reveal classified information about joint surveillance projects, according to the German weekly magazine Focus. The threat to withhold intelligence is reportedly being taken seriously by the head of the country’s federal spy agency, particularly with regards to the movements of jihadi extremists from Syria and Iraq. Gerhard Schindler, chief of the Bundesnachrichtendienst (BND), is said to have briefed Germany’s parliament on the matter Wednesday evening.

An unidentified intelligence official told Focus, “Without the information from British signals intelligence we would be blind.”

Last year, German prosecutors began investigating claims that the NSA had for over 10 years eavesdropped on German Chancellor Angela Merkel‘s telephone calls. The allegations were based on top secret documents provided by NSA leaker Edward Snowden, which stated that Merkel’s conversations, as well as those of 35 other foreign leaders, had been monitored. The parliamentary inquiry is known in Germany as the “NSA committee.”

Further damaging Washington’s relationship with Berlin was an admission by U.S. officials in July 2014 that the CIA had secretly recruited a German foreign intelligence official. The double agent admitted after arrest to spying on the Germany’s investigation into U.S. espionage activity. In response, Germany expelled a top American intelligence official from the country.

Additional reports last year indicated that the CIA is committed to monitoring wireless communication throughout Berlin’s government quarter using eavesdropping equipment at the U.S. Embassy, located just west of the grand Brandenburg Gate. Britain’s Government Communications Headquarters (GCHQ) faced similar accusations of abusing diplomatic relations to gather intelligence on German citizens—a scenario the country’s justice minister referred to as a “Hollywood nightmare.”

The British government has declined to comment on the matter, citing its longstanding policy of silence on intelligence matters. A government source said Britain was “working closely with the German government to engage with the parliamentary inquiry,” according to the Telegraph.

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