HANOVER, Germany — Der Spiegel has announced that it will press charges against a former star reporter accused of systemically faking interviews and articles, in what might be the biggest journalism scandal in Germany since another newsmagazine published fake Hitler diaries 35 years ago.

The announcement came as the United States ambassador waded into the scandal by accusing the newsmagazine of anti-American bias and calling for an independent audit.

Richard Grenell, the American ambassador to Germany, wrote a letter to Der Spiegel on Friday that appeared to try to tie the fraud committed by the reporter, Claas Relotius, 33, to the newsmagazine’s editorial methods.

Some of the most notable articles that Mr. Relotius admitted faking are set in the United States, such as profiles of a religious activist who travels the country to witness executions, anti-immigrant militiamen in Arizona and a town of Trump supporters in Minnesota.