France terror attack: Here's what we do and do not know

French authorities have opened a terrorism investigation after an attack and explosion at a gas factory that left one person decapitated and two people wounded.

What we know

President Hollande has called the attack at a factory in Saint-Quentin-Fallavier near Grenoble a "terrorist" incident in which a suspect has been arrested.

The dead man was decapitated and his head was found with messages in Arabic written on it, hanging on the fence at Air Products, a gas products firm. He has been identified as a local business man but police have withheld his name.

A "loud explosion" was heard at the factory at 9.50am local time (8.50am BST), and two people are injured. One suspect in his 30s and known to have extremist links has been arrested.

French Interior Minister Bernard Cazeneuve says multiple other people are in custody in connection with the attack.

What else has been reported

Several reports say black flags with links to Islamic terror group Isis have been found near the scene.

According to Le Dauphine Libre, a French newspaper, a source close to the investigation said a car burst into the factory site shortly before 10am (9am BST) and drove erratically around the courtyard.

AP reports that the car was carrying two people and crashed into gas canisters, setting off an explosion.

There is continued confusion over why initial reports said there were two attackers in the car, but only one man has been arrested. Police have not announced a search for a second person.

The arrested attacker has been named online as Yassin Salhi. This is currently unconfirmed.

French journalists have speculated that the second suspect could be one of the injured persons and may be arrested after treatment.

AP reports that there have been "several arrests" linked to the attack, according to a "top French official".

What we don't know

• The identity of the attacker(s)
• The whereabouts of the second person in the car
• Who the victim is
• Whether this attack was organised by Isis or another terror group
• Why the factory was targeted

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