French officials have arrested the main suspect, his accomplice and family members in connection with an attack on a gas plant. A decapitated body and its severed head were found at the scene.
"Considerable police means have been deployed," French President Francois Hollande said on the sidelines of an EU summit in Brussels, adding that all measures had been taken to avoid another tragedy.
The main suspect was arrested on the site of Air Products, the scene of the attack, Hollande said. Interior Minister Bernard Cazeneuve named the suspect as Yassin Sahli, whose wife, sister and a third person were also taken into custody.
The Air Products factory in Saint-Quentin-Fallavier, southeastern France, where the attack took place
Sahli, a 35-year-old professional driver, did not have a criminal record but was monitored from 2006 to 2008 on suspicion of radicalization. Prosecutors told the media that Sahli's vehicle was allowed to pass through the gates because he was authorized to make deliveries. CCTV cameras lost track of his movement, but picked up the van again as it drove towards a warehouse. A loud explosion was heard.
Emergency services that arrived a few minutes later found a headless body and a knife nearby. "The head was discovered hanging on the factory's wire fence, framed by two flags that included references to the shahada, or the [Muslim] profession of faith," public prosecutor Francois Molins told the press. Reuters news agency reported that the beheaded man was Sahli's boss.
The emergency workers then overpowered the suspect, who was trying to open bottles of the flammable liquid acetone.
Air Products, a US company, said its crisis teams were "working closely with all relevant authorities." The company's CEO is Seifi Ghasemi, an Iranian-born Shiite, who are considered heretics by the Sunni group "Islamic State." Security has been beefed up in all sensitive areas and will be at its highest level in the region, Hollande announced.
France also saw attacks earlier this year, when 17 people were killed by gunmen targetting the satirical weekly Charlie Hebdo and a Jewish supermarket in Paris.
mg/bk (Reuters, dpa)