The U.S. ambassador to Germany, Richard Grenell, was only a few hours into his new job when he caused a kerfuffle: A tweet he sent warned German companies about doing business with Iran.

The move offended one of Washington’s closest allies and drew sharp responses from critics in the United States. But it also strengthened Grenell’s bona fides as a Trump loyalist, the president’s “Right Hand Man in Europe,” as the far-right website Breitbart called him at the time.

Now, Grenell has picked another favorite target of the president: news media that have been critical of the United States under Trump.

Since the German newsmagazine Der Spiegel disclosed a fabrication scandal that has sent tremors through the news world at a tense time for journalists globally, Grenell has taken aim at the company.

He has tweeted about Der Spiegel, often harshly, and retweeted the criticism leveled by others, more than a dozen times in the past week.

“Spiegel hasn’t answered as to how this fraud happened,” he wrote, for example, on Dec. 23, apparently dissatisfied with the company’s somewhat extensive efforts to publicize the wrongdoings of the reporter, Claas Relotius. “It’s absurd for them to pretend this is only about one reporter.”

Grenell also got into a debate with a correspondent for the German public broadcaster ZDF, whom he told to “stop defending fake news and fabricated stories."

“We do,” the correspondent, Andreas Kynast, wrote back. “Do you?”

And Grenell wrote an incendiary letter to Der Spiegel, which it published on its site, in which he asked the company to arrange for an outside organization to conduct a thorough investigation of what went wrong.

“These fake news stories largely focused on U.S. policies and certain segments of the American people,” Grenell wrote. “While Spiegel’s anti-American narratives have expanded over the last years, the anti-American bias at the magazine has exploded since the election of President Trump."

Dirk Kurbjuweit, Der Spiegel’s deputy editor in chief, wrote a letter back to Grenell that admitted its significant lapses and apologized for Relotius’s work.

“I would, however, like to counter you on one point. When we criticize the American president, this does not amount to anti-American bias — it is criticism of the policies of the man currently in office in the White House,” Kurbjuweit wrote. “Anti-Americanism is deeply alien to me and I am absolutely aware of what Germany has the U.S. to thank for: a whole lot."

Grenell’s battle against Der Spiegel comes at a fraught time.

The respected newsmagazine has published a handful stories about the problems it said it found with Relotius’s reporting, as it continues to investigate the extent of the alleged fabrications. Relotius, 33, wrote about 55 articles for it over about four years and won numerous awards, including CNN’s “Journalist of the Year,” the European Press Prize and Forbes List of “30 under 30 — Europe: Media” award.

But the editors say they believe that most of his stories contain made-up passages, including fictional sources. Stories with sensationalized or entirely fabricated accounts included reports about a Yemeni prisoner in Guantanamo Bay, a pro-Trump town in rural America and vigilante groups along the U.S.-Mexican border, among others.

It is now doing an investigation to figure out “what happened and why.”

Earlier this week, the newsmagazine said it believed the reporter had run an improper fundraising campaign to raise money for two Syrian orphans he claimed to have met in 2016, according to Deutsche Welle.

“The fate of two Syrian children described in Relotius’s story ‘King’s children’ so moved readers that they wanted to donate to them,” Der Spiegel wrote on Saturday, according to a translation by Deutsche Welle.

But “he collected the readers' money under false pretenses, which he apparently has not, as promised, passed on,” it said.

An explainer published by Der Spiegel on the scandal also says that Relotius deceived “intentionally, methodically and with criminal intent.”

Relotius declined to comment on the case to The Post by email this week, saying that more information would come out soon.

Trump, who has made undermining otherwise credible news reporting a central effort of his presidency, has often claimed, without evidence, that reporters make up their sources.

Against this backdrop, the Relotius affair has predictably fueled a long-standing right-wing campaign to criticize media whose reporting is not friendly to Trump.

Shawn Steel, the committeeman of the Republican National Committee in California, tweeted about it on Christmas, calling it the “German Fake News” that was guilty of “hating” Trump and America.

And the right wing in Germany has done the same.

“CNN Journalist of the Year 2014 is #FakeNews. Enjoy #TeamTrump,” Germany’s far-right Alternative for Germany (AfD) party wrote last week.

Rick Noack and Luisa Beck contributed to this report.

Read more: