“I do not have a clue what he was referring to,” he said in a telephone interview. “Obviously, this could be connected to the fact that there has been a lot of negative reporting about Sweden, since Sweden has taken in a lot of refugees.”

The country processed 81,000 asylum seekers in 2014, 163,000 in 2015 and 29,000 last year, with another 25,000 to 45,000 expected this year, according to the Swedish Migration Agency.

Mr. Selin completed a study recently focusing on negative news reports about Sweden’s acceptance of refugees. It found numerous exaggerations and distortions, including false reports that Shariah law was predominant in parts of the country and that some immigrant-heavy neighborhoods were considered “no-go zones” by the police.

Breitbart News, the right-wing website once led by Stephen K. Bannon, now Mr. Trump’s senior strategist, has published numerous stories alleging that migrants have been responsible for a surge in crime and for a wave of sexual assaults. Swedish officials have said that their statistics do not justify such sweeping assertions, and that the country has a high number of sexual assault reports relative to other European countries because more victims come forward, not because there is more violence.

Mr. Selin said the news reports “were highly exaggerated and not based in facts,” adding, “Some of the stories were very popular to spread in social media by people who have the same kind of agenda — that countries should not receive so many refugees.”

As for the cover-up alleged by Mr. Horowitz, Mr. Selin said: “That kind of claim has been in the political debate for 15 years now. But nobody has been able to prove there is a cover-up. On the contrary, the fact is that crime rates are going down.”

He added: “Swedish authorities have nothing to gain from hiding the truth. We are quite keen to ensure that the debate and the story about our country is fact-based and nuanced. We are more than happy to talk about the challenges our country faces as well as the things that are going well.”