Site of Nice attack
Site of Nice attackReuters

French authorities on Sunday arrested an Albanian couple in connection with the Nice terror attack that killed 84 people last week, the Paris prosecutor's office spokeswoman told CNN.

Mohamed Lahouaiej-Bouhlel, 31, drove a 20-ton truck through hundreds gathered to watch the Bastille Day fireworks Thursday night on the Mediterranean city's waterfront.

Agnes Thibault Lecuivre, a spokeswoman for the anti-terrorism prosecutor, did not provide details on the couple's connection to the terror attack.

So far, six people have been arrested in connection with the attacks, according to CNN. Bouhlel's estranged wife was arrested at her apartment Friday and released Sunday morning without charge, her attorney told the network, adding the woman had not been in contact with the attacker since they were in the middle of divorce proceedings.

On Saturday, the Islamic State (ISIS) jihadist group claimed responsibility for the attack, saying Bouhlel was “one of the soldiers of ISIS”.

French Prime Minister Manuel Valls said on Friday that Bouhlel was “probably linked to radical Islam one way or another”, though French Interior Minister Bernard Cazeneuve said he hadn't shown up on any anti-terrorist intelligence radar.

He had no record of making militant statements and was not known to the intelligence services, the minister said.

"It seems he became radicalized very quickly," Cazeneuve said Saturday, without offering specifics.

Bouhlel, a resident of Nice, was born in Tunisia but had a permit to live and work in France, noted CNN.

He was known to police because of allegations of threats, violence and thefts over the past six years, and he was given a suspended six-month prison sentence this year after being convicted of violence with a weapon, authorities said.

Despite his criminal record, he was not on the radar for any kind of terror threat and was "entirely unknown by the intelligence services, whether nationally or locally," French prosecutor François Molins said.