The terrorist behind the Bastille Day atrocity was radicalised in a matter of weeks, French officials indicated on Saturday after the Islamic State claimed responsibility for the lorry rampage and described him as a "soldier of Islam".

Mohamed Lahouaiej Bouhlel, a loner with mental health problems, was said to have sent money to his family in Tunisia and told a van hire company "I want the heaviest truck you have" as he hastily plotted the massacre.

The attack has prompted fresh security concerns around French authorities, amid claims too few police officers were on duty when the horror unfolded on Nice's waterfront. Last night, police were still piecing together Bouhlel's terror network as they questioned five suspected associates after co-ordinated raids in Nice, including at least three in a largely Tunisian region of the city two miles from the killer's home.

Among those arrested was Harj Khalfallah, his estranged wife, who took herself to her local police station as details of the attack emerged. Police searched her 12th floor flat at Boulevard Henri Sappia and a neighbour claimed she was still in custody last night.

Bernard Cazeneuve, the French interior minister, said the attacker "appears to have become radicalised very quickly", as one neighbour of his estranged wife added: "Mohamed only started visiting a mosque in April."

The killer

Friends told police how Bouhlel had only newly grown a beard and expressed extremist views in recent weeks, authorities confirmed.

"They said he had started coming out with extremist statements and had suddenly developed an interest in radical Islam," one official source told The Sunday Telegraph.

Bouhlel's phone records prove he was in contact with known Islamic radicals. Authorities confirmed "he seems to have known people who knew Omar Diaby", an Islamist believed to be linked with the Al Nusra group, which is close to Al Qaeda.

In the days before the attack, it is said Bouhlel persuaded friends to send $142,000 in cash back to his family in their hometown of Msaken, about 20 km from Sousse, where Tunisian gunman Seifeddine Rezgui massacred 38 holidaymakers in June last year.

"Mohamed sent the family 240,000 Tunisian Dinars ($142,000) in the last few days," the attacker's brother, Jaber Bouhlel told one reporter in Tunisia.

"He used to send us small sums of money regularly like most Tunisians working abroad. But then he sent us all that money, it was a fortune."

Bouhlel's father, Mohamed Mondher Lahouaiej-Bouhlel, revealed his son had been previously prone to violence - but denied he had ever show any sign of religious extremism. He told French media he had been receiving medication from a psychiatrist after suffering a nervous breakdown in 2004.

"He became angry, he shouted, he broke anything had was in front of him," the father told France's RTLTV. "But after he went to France, nothing was done about it. It's been four years since he had been home, on special occasions his brothers and sisters would speak to him on the phone - that's it.

"What I do know, is that he never prayed, he never went to mosque, he had nothing to do with religion???? He was alone, depressed, always alone." Neighbours also described Bouhlel as an isolated figure only ever seen out on his push bike after a row with the wife of his three children.

Bouhlel, who moved to France aged 20, was prone to fits of rage and took a knife to his daughter's teddy-bear, one local said. "We often used to hear him shouting and throwing things around. When he split up with his wife, he defecated everywhere in the flat, shredded his daughter's teddy bear with a knife and slashed the mattresses."

Other neighbours said he also had periods of silence when he appeared to retreat into himself. "We never saw him bringing friends home. Sometimes he seemed depressed and hardly spoke," one said.

Bouhlel, a 31-year-old delivery driver, had a police record for violence, theft and threatening behaviour over the past six years. He was given a six-month suspended prison sentence in March after hitting a driver with a baseball bat in a road rage attack.

He was not placed on probation or kept under supervision after the incident, judicial sources said.

"His wife left him because he kept hitting her," said Hamid, an acquaintance of the killer. "He wasn't an observant Muslim. He ate pork, drank alcohol, took drugs and didn't fast during Ramadan. When I hear them saying he did this for Islam it makes me shudder. So many innocents died. It is someone's idea of a sick joke to call that guy an 'Islamist'. To me, he wasn't even a Muslim, more of psychopath."

Bouhlel plotted the rampage from his one-bed rented apartment an hour away from the promenade. He travelled 24 km out of town to pick up a 19 tonne lorry from a rental firm called Via Location, in Saint-Laurent-du-Var,

"All that we are entitled to say is that the truck was rented on Monday," an assistant at the company said yesterday, before confirming he had asked for "the heaviest truck".

At about 10.45pm on Thursday, the truck, according to witnesses, began its 2 km journey that would leave at least 84 men, women and children dead and 202 injured.

Arrests

On Saturday several raids took place less than two miles from Bouhlel's flat as police targeted the killer's "close entourage".

At least two of the homes that were raided were in a rundown, predominantly Tunisian neighbourhood, near Nice's main train station. Two people were reportedly arrested in the area, while Ramzie Arefa, 22, was arrested in a dawn raid yesterday at his family's flat on Rue Marceau, about a mile from where the deadly attacks took place.

His sister Chaima Arefa, 17, told The Sunday Telegraph that the police arrived at 6am and shot their apartment door down. "The police arrived at 6am and took my brother away," she said. "My brother is not a terrorist. We are Muslim but by he is not religious. He drinks, he smokes, he goes out."

Their mother, 49, said: "The police arrived his morning while were asleep. They fired at the door opposite. Then they fired at our door. The police turned out home upside down. They handcuffed my son and took him away. My son is innocent, I have all the proof that he is innocent." Asked why the police arrested her son she said "We are Tunisian, unfortunately for us. "

Another raid was carried out a few streets away on Rue Miollis. Fernando Jannone, 80, a neighbour, said: "I heard a boom, boom, boom and they banged on the door. The police pushed in the door and dragged someone out."

IS has previously ordered followers to drive into crowds with lorries, the modus operandi adopted by Bouhlel.

Extremist hotbed

In a statement, the news agency Amaq, which supports IS, said yesterday: "The person who carried out the operation in Nice, France, to run down people was one of the soldiers of Islamic State. He carried out the operation in response to calls to target nationals of states that are part of the coalition fighting Islamic State."

Nice has previously been described as one of southern France's "hotbeds" for extremism linked to Tunisia. More than 100 Muslims from Nice are known to have gone to Syria to join Isil.

David Thomson, an expert on Islamist terrorism, pointed out that Isil has never been known in the past to claim an attack it did not order and plan.

"Until now, they've never claimed an attack opportunistically although they could have done so many times," Mr Thomson said.

The prime minister, Manuel Valls, said on national television on Friday evening that Bouhlel was "linked with radical Islam in one way or another".

Police failings

The attack piles more pressure on the government, already under criticism for failing to stop terrorist attacks in France including the Charlie Hebdo and November 13 massacres in Paris.

Four police vans that had blocked off the Promenade des Anglais to protect a military parade were removed just hours before the attack, according to the owner of a seafront restaurant.

"I reproach the police," the owner of the Queenie restaurant, Jacques, who declined to give his surname, said. He said he had seen two police vans at each end of the beachfront avenue during a military parade in the afternoon, but they were taken away before tens of thousands of people arrived for the fireworks display.

"When you have a couple of hundred military, the Promenade is locked like a Fort Knox and when you've got a hundred thousand people, because they're civilians, the Promenade wasn't protected. It's unfair," Jacques said.

Nice has 42 municipal police and 20 soldiers were also deployed to the Riviera resort under counter-terrorism measures introduced after the November attacks in Paris. Christian Estrosi, a former mayor of Nice, said his repeated calls for more police had been ignored.

But the government said criticism that it failed to deploy enough police to Nice during Bastille Day festivities was unjustified. "The national police was present, very present, on the Promenade des Anglais," said Mr Cazeneuve.

Telegraph, UK