French Prime Minister Manuel Valls has described the attack on an Air Products factory as an act of "Islamist terrorism".
Valls, who is currently in South America, says he will hold an emergency meeting with Francois Hollande before returning to France.
"Islamist terrorism has hit France again," Manuel Valls told a press conference in Bogota, Colombia.
More top news
The Democratic presidential candidate may also have shown his cards on his choice of running mate.
The US president also shared a post on Twitter accusing Dr Anthony Fauci of misleading the public over hydroxychloroquine.
Fears over an impending second wave of coronavirus dominates Wednesday’s front pages.