PARIS (Reuters) - French police have arrested a 23-year-old cab driver after finding explosives at his home in the Seine-et-Marne district southeast of Paris, government spokesman Stephane Le Foll said on Tuesday.

The man, already known to French intelligence services and listed among thousands of people in France’s “Fiche S”, a watchlist of people suspected of posing a security risk, was arrested on Sunday night.

When police searched his home, initially on suspicion he may have burgled some of his clients, they found two sticks of dynamite, cables and detonators, as well as a picture of the Islamic State flag on his mobile phone, Le Foll said.

“Was it proof an attack was being prepared? The inquiry will tell,” he said.

The arrest came three days after an attack last Thursday in which Tunisian Mohamed Lahouaiej Bouhlel rammed a truck into crowds of Bastille Day revelers in the French resort town of Nice, killing 84, before being shot dead by police.

It was the third major attack in France in the space of 18 months. Islamic State claimed responsibility, though no hard evidence has emerged to link Bouhlel with the militant group.