French officials say they have established a Corsican link to the two explosions early on Sunday in the southern city of Nice that slightly injured 16 people.
Most people were injured by the flying glass
Top local official Pierre Breuil told the French news agency AFP that a car stolen in Corsica had been found containing bottles of petrol and a detonator near the site of the blasts.
"That confirms a Corsican lead," Mr Breuil said.
The blasts came two days after the military wing of the separatist Corsican national Liberation Front (FLNC) announced it was ending its ceasefire.
The FLNC's decision followed the conviction by a French court of eight people for assisting in the murder of the top French official on Corsica in 1998.
The first device went off outside the regional tax and customs offices at about 0230 local time (0030GMT).
The second blast happened about 10 minutes later within 50 metres of the site of the first explosion.
The injuries were caused by flying glass, when windows were blown out in nearby residential buildings.
The casualties were taken to hospital for treatment, and nearly all of them were later discharged.
Last September an explosive device was found near the Nice tax office, and defused.