The Islamic State militant group has said it was behind the massacre in Nice in which at least 84 people were killed including 10 children.

The claim of responsibility, reported by the jihadist-linked Amaq news agency, comes as five people were detained following the attack in the French resort city.

Amaq quoted an IS security source as saying one of its "soldiers" carried out the atrocity "in response to calls to target nations of coalition states that are fighting (IS)".

Mohamed Bouhlel drove a 19-ton lorry into a crowd which had been watching a fireworks display on the seafront during Bastille Day celebrations on Thursday evening.

Three men were arrested on Saturday in police raids and another was held the previous day. The driver's ex-wife has also been detained.

Sources said the arrests were centred on the attacker's "close entourage" and were made in two different areas.

About 40 elite police officers raided a small apartment at Rue Miollis, north of the central station, where one individual was arrested.

Of the 202 people injured in the massacre, 52 are in a critical condition and 25 of those are on life support.

The Department of Foreign Affairs says it has "no reason to believe" any Irish people have been caught up in the incident.

Suspended sentence for attacker

Authorities have been trying to find out whether Bouhlel, a 31-year-old French citizen born in Tunisia, acted alone or with accomplices, and whether his motives were connected to radical Islam.

His father Monthir Bouhlel said his son had undergone psychiatric treatment in the past and was unstable and sometimes violent.

French Prime Minister Manuel Valls said the killer is a terrorist probably linked to radical Islam one way or another.

But Interior Minister Bernard Cazeneuve was more guarded, saying that Bouhlel's motives were not yet known.

France's chief prosecutor Francois Molins said Bouhlel had a record for petty crime and had been sentenced to six months in jail in March for a road rage incident a few months before.

But, as the conviction was his first, the sentence was suspended.

The delivery driver and father of three "was totally unknown by the intelligence services and he had never been subject to any sign of radicalisation", Mr Molins said.

Bouhlel had driven more than a mile in the rented truck, zig-zagging across the road to mow down as many people as possible, witnesses said.

Many terrified people fled into the sea to escape the attack, with witnesses telling how people were "flying like bowling pins" as Bouhlel went on the rampage.

Mr Molins told reporters Bouhlel had shot three police officers before he was killed and his body fell onto the passenger seat.

President Hollande described the attack as a "monstrous terrorist act", declaring three days of national mourning.