French attack suspect grilled as gruesome 'selfie' emerges

French police questioned a suspected Islamist Saturday about an attack in which the man displayed his boss's severed head, as it emerged he may have sent a "selfie" of the decapitation.

Sources close to the investigation said the suspect, Yassin Salhi, a 35-year-old married father-of-three sent a picture of him with the severed head via the WhatsApp messaging service.

The message was sent to a Canadian number but investigators said they were still working to determine the final recipient, as the number used could be a relay.

Authorities are questioning Salhi about Friday's attack, during which he also drove his van into a warehouse packed with dangerous gases in an apparent bid to blow up the factory and himself.

The prosecutor in the case said firefighters overpowered Salhi as he was trying to open acetone bottles in what is believed to have been an attempt to cause a larger explosion at the US-owned Air Products factory in Saint-Quentin-Fallavier, some 40 kilometres (25 miles) from Lyon.

The firefighters then discovered the decapitated body of his 54-year-old employer Herve Cornara -- who ran a delivery firm -- near the car, along with a knife.

Cornara's head was pinned to a nearby fence.

"The head was surrounded by two Islamic flags bearing the Shahada, the profession of (the Muslim) faith," said prosecutor Francois Molins.

- Suspect begins to talk -

Salhi began speaking to investigators late Saturday, a close source to the case said.

"He had remained silent but he changed his stance... and began to explain the sequence of events," the source said.

No jihadist group has claimed Friday's attack, which came on the same day as a massacre at a Tunisian beach resort in which 38 people were gunned down and a suicide bombing in Kuwait that killed 26.

The other two attacks have been claimed by the Islamic State group.

However, sources close to the investigation said Salhi was radicalised at the start of the century after contact with a man suspected of preparing attacks in Indonesia with Al-Qaeda militants.

The first results of the autopsy on the victim did not provide the exact cause of death, nor whether Cornara was already dead before he was beheaded.

Meanwhile, in the town of Saint-Quentin-Fallavier, shocked residents held a minute's silence, followed by a pulsating rendition of France's national anthem.

One man, Philippe Ouastani, said he came to show solidarity with the victim. "It's unheard of to decapitate someone in the 21st century. What weapons do we have to combat that? Being here, together."

Another woman, wearing the Muslim headscarf, said she was "unable to speak" when she heard the news.

"These acts have got nothing to do with religion. The Prophet never said to kill innocent people," raged the woman, who requested to remain anonymous.

She tried to find words to explain the killing to her four-year-son.

"There are naughty people who have done bad things. The police will put them in prison to punish them for their silly, silly actions," she told him.

- 'Better armed' -

The gory attack in France came nearly six months after a three-day Islamist killing spree in Paris left 17 people dead, most of them gunned down in the offices of satirical magazine Charlie Hebdo.

Like the Charlie Hebdo attackers and Islamist Mohamed Merah who gunned down soldiers and Jewish children in the southwest city of Toulouse in 2012, Salhi had been known to security services for "radicalisation", but slipped through the cracks.

Interior Minister Bernard Cazeneuve said Friday Salhi had been investigated for links to radical Salafists in Lyon, but was not identified as having participated in terrorist activities and did not have a criminal record.

Speaking after a ministerial meeting on Saturday with President Francois Hollande, Cazeneuve vowed the government would "continue to work relentlessly" against terrorism.

France is on high alert over hundreds of citizens who have gone to wage jihad in Iraq and Syria, as well as those involved in recruitment or radicalisation online.

Similarly, Europe has for months been bracing for so-called "lone wolf" attacks by supporters of Islamic State, which has urged its followers to strike wherever they can.

Earlier this week, France passed a controversial new spying law granting sweeping powers to snoop on citizens.

Cazeneuve said the law allowed security services to be "better armed" to fight the jihadist threat.

Prime Minister Manuel Valls, who cut short an official trip to South America to rush home, warned France faced more attacks and that Friday's assault would increase tensions in the country, putting citizens' resilience "to the test".