Fox News anchor Bill O'Reilly has acknowledged that his show erred in seeking expert advice from a man who falsely identified himself as a Swedish national security adviser.

O'Reilly last week interviewed a man calling himself Nils Bildt during a segment on refugees in Sweden. Bildt, who was billed as a "Swedish defense and national security adviser," largely backed a narrative promoted by President Trump that portrays asylum seekers as being responsible for an increase in violent crimes in the country.

"We are unable in Sweden to socially integrate these people," Bildt said of refugees. "These things are not being openly and honestly discussed."

Just one problem: Nobody in the Swedish government has ever heard of Bildt.

"This is not a person who is known to [the government]," said Catarina Axelsson, a press officer at Sweden's foreign ministry.

Marinette Nyh Radebo, a spokeswoman for Sweden's defense ministry, said Bildt has never worked for the Swedish government or the country's armed forces.

Johan Wiktorin, the CEO of a strategic intelligence company in Sweden, tweeted that he's "never heard of [Bildt] before... he's not known in our circles as an expert."

In a statement on his program Monday, O'Reilly said criticism of his decision to book Blidt was "valid."

"[W]e looked into the situation and the criticism is valid. It's valid," O'Reilly told viewers. "Mr. Bildt does consulting work on terrorism, that's true -- but we should have clarified that he had no direct role with the Swedish government. To be fair, the information we gave you in the segment was accurate but in hindsight a more relevant guest should have been used on the anti-immigrant side. You should also know that before the segment was booked we asked the Swedish Ambassador to appear, he declined. That invitation stands."

Fox News earlier defended its decision to book Bildt.

"Our booker made numerous inquiries and spoke to people who recommended Nils Bildt and after pre-interviewing him and reviewing his bio, we agreed that he would make a good guest for the topic that evening," David Tabacoff, the executive producer of The O'Reilly Factor, said in a statement.

Related: White House blocks news organizations from press briefing

The LinkedIn profile of a person named Nils Bildt had been deleted by Monday. But a screen grab circulated online shows that the account described Bildt as a "Swedish Defense and National Adviser" who has previously worked for the Swedish Armed Forces.

CNNMoney was not able to independently verify the LinkedIn profile, or contact a person named Nils Bildt.

Swedish media outlets have reported that Bildt, who was born Nils Tolling, left Sweden in 1994 and emigrated to the U.S. He later changed his surname to Bildt.

On Sunday, the newspaper Aftonbladet reported that Bildt had expressed interest in 2013 in running for office in Sweden with the nationalist right-wing party Sweden Democrats. His bid was not successful.

The controversy over Sweden erupted when Trump made a reference to "what's happening last night in Sweden" during an early February rally in Florida.

"They took in large numbers," Trump said. "They're having problems like they never thought possible."

Related: Is the First Amendment under attack?

The comments appeared to refer to recent terror attacks in Germany and elsewhere, but no such attack has occurred in Sweden. Carl Bildt, the former Swedish prime minister, questioned the president's statement.

"Sweden? Terror attack? What has he been smoking?" Bildt tweeted. "Questions abound."

Trump later said the statement was made in reference to Swedish immigration politics. He then tweeted on the topic, saying: "The FAKE NEWS media is trying to say that large scale immigration in Sweden is working out just beautifully. NOT!"

The Swedish embassy in the U.S. said it was looking forward to "informing the U.S. administration about Swedish immigration and integration policies."

-- Brian Stelter and Dylan Byers contributed to this report.