German counterintelligence has intensified its surveillance of “certain employees of the United States embassy” in Berlin, after internal reports suggested that “up to 20” agents of the American government are operating inside the German federal bureaucracy.

Citing information “from American security circles”, German newspaper Bild am Sonntag said on Sunday that the agents are German citizens who are secretly employed by a variety of American civilian and military intelligence agencies in return for money. The Berlin-based tabloid noted that at least a dozen such agents have infiltrated four departments of the German federal government, namely the Ministries of Defense, Finance, Interior, as well as the Ministry for Economic Cooperation and Development. The paper said that the latter has been targeted by the US Central Intelligence Agency because it is routinely employed by the BND, Germany’s main external intelligence organization, as a cover for clandestine activities.

Last week, Germany ordered the immediate removal from the country of the CIA station chief, after it caught two German citizens, one working for the BND, and one for the country’s Ministry of Defense, secretly spying for Washington. It also instructed its intelligence agencies to limit their cooperation with their American counterparts “to the bare essentials” until further notice.

According to Bild am Sonntag, the “growing pressure” against American intelligence operations inside Germany has prompted American spy agencies to transfer their recruitment activities of German citizens to nearby European capitals, such as Prague of Warsaw. Meanwhile, in an interview aired Sunday on Germany’s public-service television broadcaster, ZDF, German Chancellor Angela Merkel appeared pessimistic about the possibility that American intelligence agencies will stop recruiting German citizens. She said that Washington and Berlin had “fundamentally different views” on the nature and operational character of intelligence, and that it would be difficult to bridge the gap of perception between the two countries. The German leader added, however, that she favored continued cooperation between German and American intelligence agencies, as both countries “profit from the cooperation concerning counterterrorism and other things”.

Germany’s Foreign Affairs Minister, Frank-Walter Steinmeier, is scheduled to meet Monday in Vienna with US Secretary of State John Kerry. The meeting agenda is devoted to the ongoing international negotiations on Iran’s nuclear program, but Steinmeier told German media over the weekend that he planned to raise Germany’s concerns about American espionage with his American counterpart. Washington has refused to comment publicly on the issue, saying that it should be addressed though discrete diplomatic channels, not publicly through the media.