The Islamist gunmen behind a wave of terror attacks in Paris last week purchased their weapons from a Belgian arms dealer located in Brussels, Belgian media reported.
The dealer turned himself in to police on Tuesday.
"The man is being held by the judge in Charleroi on suspicion of arms dealing," a spokesman for Belgium's federal prosecution said. "Further investigations will have to show whether there is a link with the events in Paris," he added.
Police discovered papers linking him to a transaction with Amedy Coulibaly, the Islamist who killed four Jewish men at the Hyper Cacher supermarket in Paris on Friday.
According to the report, the man sold Coulibaly the Skorpion submachine guns used in the supermarket attack, in addition to a grenade launcher and Kalashnikov rifles that the Kouachi brothers used in the attack at the Charlie Hebdo magazin in which 12 people were killed. The transaction took place in downtown Brussels near the Midi railway station and the arms were purchased for just under 5,000 euros ($5,900).
Coulibaly got the money for the weapons from a $7,000 loan he took out in early December from French financial-services firm Cofidis, the French newspaper Le Parisien said on Wednesday.
He presented a false statement of his monthly income in order to get the loan, but used his real name during the transaction.
The Belgian arms smuggler from the town of Charleroi confessed to police he had sold weapons as well as a car to Coulibaly.
During a search of his house police found documents indicating Coulibaly wanted to buy weapons and ammunition, including a Tokarev pistol of the sort used by the Frenchman during the supermarket attack, it said.