President Trump said that more journalists could be barred from the White House following the decision to rescind the credentials of CNN reporter Jim Acosta.

Speaking to reporters on the South Lawn of the White House before leaving for Europe, Trump said that "this is a very sacred place to be" and that journalists did not have a guaranteed right to work there. "You've got to treat the White House and the office of the presidency with respect," he said.

Trump singled out April Ryan of American Urban Radio Networks, saying that "she's very nasty and she shouldn't be." He has often clashed with Ryan, a persistent Trump critic who last year became a CNN contributor, and was irked this week when she tried shouting out questions to him at his free-wheeling Wednesday press conference.

"Talk about somebody who’s a loser," Trump said outside the White House before a trip to Europe. "She doesn’t know what the hell she’s doing."

Ryan responded on CNN afterward, calling Trump's comments about her "terrible."

[Also read: White House move against Jim Acosta just the latest rebuke to CNN]

Ryan was unsuccessful in getting in a question at the conference Wednesday, which came one day after the midterm elections. Trump did not call on Ryan but she tried shouting out anyway and Trump told her she was being rude.

The press conference saw multiple clashes between Trump and reporters, CNN's Jim Acosta in particular.

Ryan has been critical of the Trump administration and its staff, once suggesting that White House press secretary Sarah Sanders had threatened her and also that Trump harbors racist sentiments.