AFP/Paris

French investigators were on Wednesday interrogating a knife-wielding man who attacked three soldiers outside a Jewish centre in Nice, as questions resurfaced over security measures a month after the Paris attacks.

The attacker, identified as 30-year-old Moussa Coulibaly from the poor western suburbs of Paris, was already known to police who questioned him just days before the attack, when he was turned away from Turkey last week.

Police arrested him immediately after he knifed the soldiers in broad daylight while they were patrolling outside the Jewish centre as part of reinforced security measures introduced after last month's jihadist attacks in Paris that left 17 people dead.

Prime Minister Manuel Valls announced that the highest security level, in place in the Paris region since the attacks, would be extended to the Alpes-Maritimes province where Nice is located.

"This attempted murder targeted soldiers because they were soldiers," Defence Minister Jean-Yves Le Drian said during a visit to the victims' barracks.

Two of the troops received knife wounds and a third managed to tackle the assailant to the ground.

Anti-terrorist police were focusing their investigation on whether Coulibaly had known the soldiers were protecting a Jewish centre, tucked away in a courtyard in the French Riviera city, and what his motives were.

A rabbi, Franck Teboul, visited the Jewish centre Wednesday and said: "It is likely the centre was not targeted."

Police were also questioning Coulibaly's mother, sister and brother who were taken in after a search of his home in the Parisian suburb of Mantes-la-Jolie.

Since returning from France after his expulsion from Turkey on January 29, Coulibaly was staying at a hotel near Nice station, where investigators found a handwritten document on religion as well as Turkish currency.

- Well-known to police -

The knifeman has not been linked to Amedy Coulibaly, who killed a policewoman and four Jewish shoppers in a kosher supermarket during the Paris attacks last month before being shot dead by police.

The surname is extremely common in west Africa.

Moussa Coulibaly had already been fined and given suspended jail sentences in France for offences including robbery and drug use.

He was picked up and questioned in mid-December after "aggressively" trying to spread his beliefs in a gym in Mantes-la-Jolie, a source said.

French intelligence services were then alerted to the fact that he was trying to enter Turkey -- a key entry point for jihadists seeking to go to fight in Syria -- and asked the country to expel him.

However he was released as there was not enough evidence to press charges.

"We can't consider it a failure every time that security forces mobilise over individuals likely to radicalise... but legal action is not taken due to lack of proof," said Interior Minister Bernard Cazeneuve.

Coulibaly again fell foul of the law shortly before the attack, when he was fined for not having a ticket on a tram, and a Chad-born Canadian seen with him was taken into custody, although no formal link has been made between the two men.

"We don't know what was going on in his head... he is normal," a man who introduced himself as Coulibaly's brother told journalists during the police search of his home on Tuesday.

- Massive security measures -

The attack came after France beefed up security to unprecedented levels around the country -- deploying some 15,000 police and troops to protect sensitive sites in the wake of the Paris attacks.

Valls warned of the task facing security forces who have to monitor some 3,000 people with links to jihadists or "terrorist networks" in Syria and Iraq.

The three men who carried out the coordinated January 7-9 attacks in Paris had also been known to police and Valls admitted there had been security "failings".

France is battling to curb the flow of jihadists heading to fight alongside the Islamic State group, fearing they will carry out attacks on their return.

IS made fresh threats against France on Tuesday, because of its involvement in a US-led coalition carrying out air strikes against the jihadist group.

A video widely shared online showed a masked jihadist urging the French to join their fight, and called on supporters to attack police and military targets in France.