WASHINGTON - U.S. President Donald Trump launched a new attack on the country's national news media Wednesday, suggesting that maybe their credentials should be taken away, while also admitting that when he talks about "fake news," he means stories about him he doesn't like.

"The Fake News is working overtime," Trump said in a Twitter comment. "Just reported that, despite the tremendous success we are having with the economy & all things else, 91 percent of the Network News about me is negative (Fake). Why do we work so hard in working with the media when it is corrupt? Take away credentials?"

Trump was citing a report by the conservative-leaning Media Research Center concluding that from January to April more than nine in 10 Trump-related stories on the ABC, NBC and CBS television networks were critical of him. The three broadcast networks have nightly news shows, but millions of Americans also hear national news on cable television networks, social media and word of mouth from friends and relatives.

In the U.S., the First Amendment to the Constitution guarantees freedom of the press, and dozens of reporters carry credentials that allow them on White House grounds to report and write about Trump. U.S. presidents often spar with reporters about stories they do not like, but Trump has waged a concerted campaign against several news sources, particularly the three networks, the cable news outlet CNN, The New York Times and The Washington Post, while often praising commentary shows on the Trump-friendly Fox News.

The U.S. leader has often attacked national news media reports about his nearly 16-month tenure in the White House that he deems unfair, unsourced or not reflecting reality as he sees it. Wednesday's tweet, however, may be the first time he has acknowledged that he thinks negative news about him is "fake."

After Trump's tweet, Margaret Talev, president of the White House Correspondents Association, said in a statement that if Trump were to carry out his threat and revoke White House credentials for reporters, it would be “an unconscionable assault on the First Amendment.”

“Some may excuse the president’s inflammatory rhetoric about the media, but just because the president does not like news coverage does not make it fake,” she said. “A free press must be able to report on the good, the bad, the momentous and the mundane, without fear or favor.”