The man, whose name was not released, was arrested in southern France a week ago, and had been the target of an expulsion order since July 18, the ministry said.

It did not specify why the man had been arrested and later sent to the German city of Kehl, just across the Rhine river from the northeastern French city of Strasbourg.

French authorities are boosting security in Biarritz during the Group of Seven meeting of major industrialised nations, including blocking off large parts of the city after activists announced plans to hold a "counter-summit" nearby with thousands of demonstrators.

In an interview with Germany's Radio Dreyeckland, which had hired him to report on the G7 summit in Biarritz from August 24-26, the man accused French Interior Minister Christophe Castaner of trying to keep "annoying people" far from the summit.

On August 8, "after being stopped at a police checkpoint, I was arrested and spent 24 hours in jail because I had been designated a leftist activist, even though they didn't give any reason at first," said the man, identifying himself as Luc.

"They told me I had been identified for the first time a year and a half ago in Bure," where France is preparing to bury radioactive waste from its network of nuclear power plants, he said.

He also said police suspected him of offences during the G20 in Hamburg, Germany, in July 2017, "even though there has been no conviction: the investigations are still under way," he said.

The Hamburg summit was marked by acts of violence and clashes between far-left protesters and police.

He said he had hired a lawyer to contest his expulsion.

French President Emmanuel Macron made clear in a preparation visit last May to Biarritz, one of the jewels of France's Basque country, that security measures would be "unprecedented".