PARIS—French authorities in Paris are searching an Air France airplane that arrived from Chad following an anonymous threat about a possible explosive device on board, officials said on Thursday. Air France said in a statement that following the threat, Air France Flight AF865 from N’Djamena to Paris had been escorted by a French Air Force fighter plane and had landed at the Paris-Charles de Gaulle airport. Interior Minister Gerard Darmanin said in a tweet that due to the suspected presence of an explosive device aboard the plane, an investigation had been started.