France, Sept. 25 -- Riner, a multiple Olympic and world champion judoka, is one of French sport's most popular figures.

During an interview with sports television show Stade 2 last week, he said he was "freaked out" by the rise of extremism.

Asked if he meant "on both sides" - meaning the far left and the far right - Riner replied: "The far right."

France's presidential election is being held next April and Marine Le Pen's far-right, anti-immigration National Rally party is polling ahead.

Following the interview, Riner received numerous racist insuts and hate messages online, the Public Prosecutor's Office said.

In a brief statement posted on Instagram on Wednesday, the office said it had opened an investigation into "racist insults ...