The French government said Wednesday that a researcher had been prevented from entering the United States, where he planned to attend a scientific conference in Texas.

"This measure was apparently taken by the American authorities because this researcher's phone contained exchanges with colleagues and friends in which he expressed a personal opinion on the Trump administration's research policy," said Philippe Baptiste, the French minister of higher education and research.

But a spokesperson from the Department of Homeland Security said in a statement to AFP that "any claim that his removal was based on political beliefs is blatantly false."

The spokesperson said "the French researcher in question was in possession of confidential information on his electronic device from Los Alamos National Laboratory -- in violation of a non-disclosure agreement -- something he admitted to taking without permission and attempted to conceal."

The Los Alamos National Laboratory, located in New Mexico, was founded by Robert Oppenheimer during World War II to develop the atomic bomb, and still conducts research on nuclear weapons.

According to a French diplomatic source, the space researcher was subjected to a random check upon arrival, during which his work computer and personal phone were searched.

He was allegedly accused of posting messages "that convey hatred toward Trump and can be classified as terrorism." His professional and personal equipment was reportedly confiscated, and he was sent back to Europe on March 10.

Since returning to the White House, Donald Trump has targeted the scientific community, cutting research budgets, imposing conditions on universities, and censoring certain subjects in funded research.

The French Academy of Sciences on Friday called on international scientific institutions to "denounce an authoritarian drift that is harmful to science."