The French government’s claim that a scientist was denied entry into the United States because of an opinion he expressed about the Trump administration is “blatantly false,” a U.S. official has said.

Even as the authorities in France continued to call the case a concerning violation of academic freedom, the U.S. official, Tricia McLaughlin, who is a spokeswoman for the Department of Homeland Security, said the scientist had been turned away for reasons unrelated to his personal beliefs.

“The French researcher in question was in possession of confidential information on his electronic device from Los Alamos National Laboratory — in violation of a nondisclosure agreement — something he admitted to taking without permission and attempted to conceal,” Ms. McLaughlin said late Thursday.

Philippe Baptiste, the French minister for higher education, said this week that the scientist, who has not been publicly identified and who specializes in outer space research, was traveling to a conference near Houston earlier this month.

The scientist was not allowed to enter the United States, Mr. Baptiste said, because his phone contained message exchanges with colleagues and friends in which he gave his “personal opinion” on President Trump’s scientific and research policies.

But Ms. McLaughlin rejected that assessment. “Any claim that his removal was based on political beliefs is blatantly false,” she said. She did not provide further details.

It was unclear when or how the scientist might have worked at or interacted with the laboratory at Los Alamos, N.M.

Los Alamos National Laboratory is best known as a place that was crucial to the development of the atomic bomb.

Today, it is a top research facility for the National Nuclear Security Administration, but it also conducts scientific work on other topics. Representatives for the laboratory were not immediately reachable for comment.

The scientist was working for France’s publicly funded National Center for Scientific Research. Representatives for the center said that he did not wish to speak to the media, but they did not immediately respond to the Department of Homeland Security’s allegations against him.

Neither did the office of Mr. Baptiste, who used to lead the French National Center for Space Studies before he became minister in 2024.

But on Friday, Mr. Baptiste repeated his claim that the scientist had been targeted because of private discussions and opinions about the Trump administration’s policies.

He told Sud Radio in an interview that he had not spoken with the scientist directly but that his ministry was in touch with him.

“Each country is free to regulate their borders,” Mr. Baptiste acknowledged. But he said the scientist’s case was “extraordinarily atypical” and a “subject of concern.”

That concern was shared by the French Academy of Sciences, which said in a statement on Thursday that the scientist’s deportation “seriously undermines the fundamental freedoms of the academic world: freedom of thought, expression and travel.”

Zolan Kanno-Youngs contributed reporting from Washington D.C., and Ségolène Le Stradic from Paris.