Prosecutor Diane Ngomsik told AFP news agency that the 18-year-old volunteer firefighter initially confessed to having “set twigs on fire with a lighter and gasoline” before recanting.

BFMTV said a second 18-year-old man had also been placed under formal investigation, a stage of French criminal procedure that can lead to formal charges and a subsequent trial.

The Fontainebleau forest fire partially closed the country’s main north-south highway since it began last Sunday.

President Macron claimed that 10% of the forest had burned and praised the fact that there have been no casualties so far.

The forest is home to the Fontainebleau Palace and Park, declared a World Heritage Site by UNESCO since 1981.

France has recorded nearly 11,000 fires since the beginning of the year.