An attack occurred at a US-owned gas factory in the city of Saint-Quentin-Fallavier near France city of Lyon, leaving one dead and two injured.
"Due to the terrorist attack, the level of terrorist threat in in the [Rhone-Alpes] region will remain maximum for three days," Hollande said following an emergency meeting of the French Security Council, as French BFMTV reported.
Earlier on Friday, the president urgently left EU summit in Brussels to return to Paris, after two individuals in a car reportedly crashed through the gates of the factory, hitting tanks containing gas that caused an explosion. Investigators found a decapitated body and an Islamist flag at the scene of the incident.
The suspects are said to have been detained.