Double arrest made in French Nice attack probe
The man and woman are expected to join five others who are already held in police custody, including the wife of driver, Mohamed Lahouaiej Bouhlel.
Mohamed Lahouaiej-Bouhlel, 31, rammed a 19-tonne truck into a large crowd as July 14 fireworks were ending in the French Riviera city, before being shot dead by police.
The Tunisian is said to have no apparent links to extremism but authorities suggest he was radicalised very quickly.
At least 10 children were among the dead and 50 more were wounded, some of them critically, a hospital official said.
On Saturday, the Islamic State group claimed responsibility for the truck attack that killed 84 people in Nice.
The statement from al-Bayan said an IS "soldier" carried out a "new, special operation using a truck" to cause Thursday's carnage.
Al-Bayan warned that Western countries "will not be spared from the blows of the mujahideen" no matter how much they increase their security measures.
Earlier, the IS-affiliated Amaq news service quoted a security source as saying the attack was "in response to calls to target nations of coalition states that are fighting (IS)".
IS has called on its supporters living in Europe to carry out lone-wolf attacks on Westerners, publishing a video early this year called "Kill wherever you find them."
French President Francois Hollande said in the wake of the Nice attack that France would strengthen its role in Iraq and Syria, where it is part of a US-led coalition fighting the extremists.