A 42-year-old Frenchman suspected of plotting attacks with two Belgian brothers was charged with terror offences on Sunday, a judicial source said.
The source said the man, known to authorities before his arrest, was charged with arms possession and having links to extremist groups.
The suspect is believed to be connected to Akim and Khalid Saouti, two brothers charged in Brussels on Wednesday with belonging to a "terrorist group". They were believed to be planning an attack with a large stash of weapons including Kalashnikov rifles.
The pair, arrested the previous night in the Brussels suburb of Anderlecht, are brothers of convicted jihadist Said Saouti, a member of the Kamikaze Riders, a notorious bikers' club based in the Belgian capital.
Last year, Saouti was jailed for six years for recruiting people to jihadist organisations and supporting the Islamic State (IS) group on social media.
A source close to the probe said authorities feared the three men were planning "an imminent attack in France or Belgium."
The French suspect has been jailed four times for acts of violence and theft and was put under surveillance after leaving prison in May 2015 where he was believed to have been radicalised.
He was then observed making several trips to Belgium, where he met the Saouti brothers with all of them seen handling bags at a garage in Anderlecht.
France and Belgium have suffered a string of deadly attacks claimed by the Islamic State group in recent years.