Demand for air travel to France, and Nice in particular, has dropped again after an attacker killed 84 people in the city on the French Riviera on July 14, according to travel data analysis company ForwardKeys.

France's tourism industry had yet to fully recover from assaults in Paris in January and November last year, which were also claimed by Islamic State, when Mohamed Lahouaiej Bouhlel drove a truck into a crowd on Nice's Promenade des Anglais.

Daily net international bookings to Nice for future arrivals, combining cancellations of previous bookings and a decline in new bookings, dropped by 57 percent in the period July 15-23, compared with the previous year, ForwardKeys said.

ForwardKeys said flight bookings for travel in August and September were already down before the July attack but have since taken another knock.

Bookings for travel to Nice for August and September were down 14 percent compared with last year before July 14, but are now down 19 percent, while bookings for France as a whole are down 20 percent, compared with a drop of 16 percent before July 14.

"Ever since the Charlie Hebdo attack last January, France has been suffering from a reduction in tourism confidence and just as bookings started to recover, another attack has taken place," ForwardKeys chief executive Olivier Jager said in a statement.

Air France-KLM on Wednesday raised concerns over the attractiveness of France as a destination, saying the attacks were hurting demand from Japan, China and the United States.