President Trump used the global stage to call an unfavoured cable news network "fake news" on Friday, at a joint press conference with British prime minister Theresa May.
During a question and answer session after both leaders had delivered short speeches, Jim Acosta of CNN attempted to ask the president about taxes but was cut off.
"That's fake news, I don't take questions from CNN, CNN is fake news, I don't take questions from fake news," the president said.
Trump also criticised NBC after its reporter asked him about his forthcoming meeting with Russian president Vladimir Putin, calling the journalist "dishonest" and the network "possibly worse than CNN".
He then took a question from Fox News, which he called "a real network".
John Roberts, the Fox reporter, said in an emailed statement that he supported his White House press corps colleagues and that it was unfair to marginalise them.
"In today's press conference, I paused while my colleague from CNN went back and forth with President Trump over a question," he said. "When it became clear that the president wasn't going to entertain a question from him, I proceeded with my question, as did my fellow colleagues in the press corps.
"I know Kristen Welker of NBC. She is honest as the day is long. For the President to call her dishonest is unfair. I also used to work at CNN. There are some fine journalists who work there and risk their lives to report on stories around the world. To issue a blanket condemnation of the network as 'fake news' is also unfair."
Trump and his supporters have a long history of goading or ignoring CNN, as well as other news outlets. Trump has refused to take Acosta's questions before, and just last month the reporter was booed and told to "Go home, Jim!" at a Trump rally in South Carolina.
But Trump, despite his assertion that he never takes questions from CNN, did so yesterday. After he'd had made some strong comments about Germany's defence spending and reliance on Russia at the NATO summit in Brussels, the president was asked by CNN's Jeremy Diamond about the commitments he said he'd secured.
Trump gave a fulsome answer, complaining that the US was paying far too much towards NATO budgets and Germany not enough.
Hadas Gold, a CNN reporter, said on Twitter that by bypassing disliked news outlets on foreign soil Trump had given encouragement to authoritarian leaders to restrict press freedom, a view shared by others in the media industry.
Feuds between media outlets and presidents are not new. President Obama was openly critical of Fox News and its nakedly negative coverage of his administration – but attempts to ban its reporters from government press briefings were resisted and widely criticised by other media outlets.
In 2009, officials had attempted to omit Fox News from a Treasury briefing, but other networks refused to take part until its journalists were allowed in.
CNN declined to comment.