German political outrage mounted Sunday as Interior Minister Thomas de Maiziere demanded a swift explanation from Washington regarding spying allegations.

An employee of the German Foreign Intelligence Service (BND) was arrested last week and accused of working as a double-agent for the United States, turning over 218 secret documents. Der Spiegel reported he was caught after intelligence officials came across an e-mail in which the suspect allegedly offered his services to Russia.

“I expect everyone to co-operate promptly to clear up these allegations -- with quick and clear comments from the United States as well,” de Maiziere told Bild.

German President Joachin Gauck said Saturday on ZDF television if the allegations against the accused double-agent prove true, "it's the point where I'd say it's finally enough."

U.S. Ambassador John Emerson was summoned by the Foreign Ministry Friday to discuss the situation.

A national poll to be published Monday in Spiegel indicates 56 percent of Germans want greater independence from U.S. influence and 69 percent said trust in the United States as an ally has faded, the Financial Times reported.

Germany already is investigating the extent of U.S. spying by the National Security Agency. The inquiry was prompted by revelations by Edward Snowden of NSA monitoring of Chancellor Angela Merkel's cell phone.