France’s research minister said a French scientist was denied entry to the US this month after immigration officers at an airport searched his phone and found messages in which he had expressed criticism of the Trump administration.

“I learned with concern that a French researcher” on assignment for the French National Center for Scientific Research (CNRS) “who was traveling to a conference near Houston was denied entry to the United States before being expelled”, Philippe Baptiste, France’s minister of higher education and research, said in a statement on Monday to Agence France-Presse published by Le Monde. “This measure was apparently taken by the American authorities because the researcher’s phone contained exchanges with colleagues and friends in which he expressed a personal opinion on the Trump administration’s research policy,” the minister added.

A diplomatic source told the French news agency that the incident occurred on 9 March. Another AFP source said that US authorities accused the French researcher of “hateful and conspiratorial messages”. He was reportedly also informed of an FBI investigation, but told that “charges were dropped” before being expelled.