A French national appeared in court on Sunday on charges of plotting a terrorist attack. The 42-year-old was planning the plot with two Belgian brothers who were charged in Brussels this week, judicial sources said.

According to a source close to the enquiry, the man — whose name was not given but who was known to the authorities for being radicalized — was arrested near the northern city of Lille.

Paris prosecutors have opened an inquiry on grounds of terrorist conspiracy.

The suspect is believed to be connected to Akim and Khalid Saouti, two brothers who were charged in Brussels on Wednesday with belonging to a “terrorist group” and were believed to be planning an attack with a large stash of weapons including Kalashnikov rifles.

The pair, who were arrested the previous night in the Brussels suburb of Anderlecht, are brothers of convicted extremist Said Saouti, a member of the Kamikaze Riders, a notorious bikers’ club based in Brussels.

Last year, Saouti was jailed for six years for recruiting people to jihadist organizations and supporting the ISIS terrorist group on social media.

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 radicalized.

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.

“The fear of an imminent attack in France or Belgium led to a wave of arrests,” a source close to the probe said, referring to last week’s raids.

Inside the garage, they found a box containing three Kalashnikov rifles, a pump-action shotgun, three handguns, four detonators and ammunition as well as uniforms from the police, the security forces and the emergency services.

One of the bags they were seen handling was found at the French suspect’s home, containing several kilos of jewels, the source said. Investigators also found extremist propaganda and footage of suicide attacks on his computer.

Investigators from a joint Franco-Belgian operation had on Wednesday confirmed arresting a 42-year-old man just outside Lille on suspicion of links to the Kamikaze Riders who was planning a “violent attack”.

Meanwhile, Italian police said on Saturday they had arrested a Chechen man suspected of being an ISIS terrorist. He was suspected of involvement in attacks in the Chechen capital Grozny in 2014.

The 38-year-old man is accused of crimes of international terrorism and is now in prison in the south Italian town of Foggia, a police statement said.

The man, called Eli Bombataliev according to a court document, is believed to be linked with 2014 clashes in the capital of Russia’s southern province of Chechnya, in which media offices and a school were burnt and which left at least 20 dead, the police said.

The investigations started out of a collaboration with Belgium, where the man was part of a network of people who recruited foreign fighters.

“The moment (he) left (Russia) he started wandering in Europe, counting on the fact that he had a refugee status… he then reached Syria where he fought between 2014 and 2015,” prosecuting magistrate Giuseppe Gatti, who worked on the case, said in a televised news conference.

Some 450 people have left Belgium to fight in Syria and Iraq, the highest country contribution in Europe on a per capita basis. Returning Syria fighters have also been involved in militant attacks in Belgium, France and elsewhere in Europe.