Broadcaster NDR reported on Thursday that according to unnamed sources, public prosecutors in Berlin are investigating employees of the Chancellery in their search to find who sent confidential documents to WikiLeaks.
But the sources stressed that the investigation does not necessarily mean that there is a concrete suspicion against any individual employee.
Government sources also told Reuters that the Chancellery had agreed weeks ago to the investigation against "unknown" persons, but added that there are no firm suspicions against Chancellery officials.
Spiegel had previously reported that the Bundestag (German parliament) was also under investigation.
The investigation surrounds thousands of documents published by WikiLeaks in December relating to a German parliamentary inquiry into the spying collaboration between the US National Security Agency (NSA) and the German BND intelligence agency.
Many of the documents were deemed “only for official use” - the lowest level of secrecy classification.
The parliamentary committee was established in 2014 in the wake of the Edward Snowden leaks that revealed the extent of the NSA’s surveillance worldwide. The revelations caused tensions in Germany with the US after it was reported that Merkel’s own phone had been tapped.
But further leaks also unearthed the relationship between German and US intelligence, and how the BND helped the NSA spy on allies.
The documents released by WikiLeaks had been accessible to all MPs on the parliamentary inquiry committee, as well as to their subordinates, NDR reports. Sources within parliamentary circles told NDR that significantly more than half of these workers had regularly copied the complete database of the inquiry committee.
The chair of the NSA committee Patrick Sensburg told NDR that he agreed that there should be a wider investigation.
“One cannot only take MPs into consideration, but must also consider the executive,” Sensburg said.
Die Linke (Left Party) committee member Martina Renner added that she found it “astonishing” that prosecutors only now want to investigate the federal government.
“That many more people had access to the published documents is not something that was only found out yesterday,” Renner told NDR.
Employees of the Chancellery also had regular access to transmitted committee data, and could copy this information onto a hard drive for their own inventories, for example, to be able to examine meeting records, NDR reports.
It is not clear whether the prosecutors have already interviewed witnesses or examined further documents. A Chancellery spokesperson declined to comment further to NDR.