At least one man attacked a U.S. gas factory Friday in southeastern France, posting a severed head at the factory's entrance along with banners covered with Arabic writing, officials said. France immediately opened a terrorism investigation.

President Francois Hollande, speaking in Brussels, said one person was killed and two injured in the attack, which began shortly before 10 a.m. when a car crashed the gate of a gas factory in Saint-Quentin-Fallavier, about 30 kilometers (20 miles) southeast of Lyon.

The car then plowed into gas canisters, touching off an explosion, he said.

"No doubt about the intention — to cause an explosion," Hollande said, calling the attack "of a terrorist nature."

The French president said a suspect has been arrested and identified, and indicated that a second attacker might have been involved.

The industrial site belongs to Air Products, an American chemical company based in Allentown, Pennsylvania.

The attack bore the hallmarks of Islamist militants.

A security official said a decapitated head was found posted on the gate at the entrance to the factory, in what appeared to be an echo of Islamic State's practice of beheading prisoners and displaying the heads for all to see.

Two flags, one white and one black, both with Arabic inscriptions, were found nearby, the security official said.

The official, who spoke on condition of anonymity because he was not authorized to release details to the media, said the head's body was found near the site of the explosion but the victim was not decapitated by the blast.

France's anti-terror prosecutor said an investigation was opened into the attack, which he said was carried out by "a terrorist group."

French Interior Minister Bernard Cazeneuve was heading to the site.

Hollande spoke after watching TV news reports about the attack with German Chancellor Angela Merkel as both leaders attended a European Union summit in Brussels.

France went on high alert after attacks in January against the satirical newspaper Charlie Hebdo, a Jewish grocery store and a policewoman that left 20 people dead in the Paris region, including three Islamic extremist attackers.

French media said the government had ordered security to be stepped up around sensitive sites in the surrounding Rhone-Alpes region.

The Associated Press and Reuters were used in this report.