'Knifeman who attacked police may have had Isis links' - French police

French antiterrorist police have launched an investigation, after a man shouting "Allahu akhbar" stabbed three police officers in a police station, before being shot and killed by police.

The man, who has been named as Bertrand Nzohabonayo, attacked the officers yesterday in Joue-les-Tours, the largest suburb of Tours, central France.

A French citizen of Burnundi origin, law enforcement said he may have been radicalised by Islamist preachers online.

He was well known for his radical positions, and had an Islamic State flag on his Facebook page, but was not on the French intelligence's terror watch list, reports RFI.

"It looked like the sort of act called for by Islamic State," a source close to the investigation told the agency.

Security has been stepped up at police and fire stations across France.

Antiterror investigators of Paris' prosecutor's office have opened an inquiry for "attempted murder and criminal conspiracy in connection with a terrorist organization".

Local prosecutor Jean-Luc Beck said investigators would seek to determine whether "he acted alone or if he acted on orders".

A source told RFI that the man's brother was known to police, and may have planned to travel to Syria to fight for Isis.

French interior minister Bernard Cazeneuve described the attack as "extremely violent" and emphasised that the investigation was in its early stages.

A witness told AFP he saw four officers grab Nzohabonayo to escort him inside the station, while telling him to "calm down" as he started yelling and struggling.

"I saw a large knife, and then a policeman on the ground with his neck full of blood, squirting blood," Sandgy Dumoulin said.

"Then a policewoman had blood on her head, and a third one — he's the one who fired the shots. He fired four shots."

None of the three officers was killed in the attacks.

In November, Islamic State released a video showing four militants burning their French passports, and calling for supporters to bring terror to the streets of Europe.