A French scientist has been denied entry into the United States, apparently for a personal opinion on U.S. President Donald Trump's policy on research, it was reported Thursday.

The scientist had his work laptop and smartphone combed through at the U.S. border on Wednesday and denied entry. The scientist was deported on the following day, reported Agence-France Presse (AFP), quoting a diplomatic source.

U.S. agents found messages about the treatment of scientists under the Trump administration that "showed hatred toward Trump and could be qualified as terrorism", the source was quoted as saying.

French Higher Education Minister Philippe Baptiste told the AFP that the French researcher on assignment for the French National Center for Scientific Research was traveling to a conference near Houston, Texas.

"This measure was taken by the U.S. authorities because the researcher's phone contained exchanges with colleagues and friends in which he expressed his political opinion on the policies of the Trump administration on research," said Baptiste on Wednesday.