Salah Abdeslam, in custody in France over the November 2015 attacks that left 130 people dead, has refused to cooperate with French judges ever since his arrest five months after the atrocities.

A Brussels court on April 23 sentenced Ayari and Abdeslam to 20 years in prison for trying to kill police officers.

The court in the Belgian capital said "there can be no doubt" about jihadist Salah Abdeslam and his co-defendant Sofiane Ayari's involvement in extremism.

The prime surviving suspect in the Islamic State attacks in Paris that killed 130 people refused to answer questions when his trial for a later shooting incident opened on Monday in Belgium.

Paris attacks suspect Salah Abdeslam's lawyer asked on Wednesday for his client's trial in Belgium to be postponed from next week's opening, a source close to the investigation said.

With Islamic State losing ground in Iraq and Syria, hundreds of French citizens - and in some cases their children - are expected to attempt to return to France, leaving the government in a quandary over how to deal with them.

Christine Riviere, 51, dubbed by investigators as "Jihadi Gran", was arrested in 2014 after three trips to Syria, which she said were aimed at spending time with her son in case he was killed.

Four people including a 16-year-old girl were arrested on Friday by anti-terrorist police in Montpellier in southern France on suspicion of preparing an attack, a police source said.

Belgium has charged two suspects with providing false documents to a man linked to the November 2015 Paris attacks, who later blew himself up on a crowded Brussels metro, federal prosecutors said on Thursday.

Police have broken up a terror ring plotting an attack in France after arresting seven suspects in Strasbourg and Marseille, Interior Minister Bernard Cazeneuve said on Monday.

Lawyers for the main suspect in the Paris attacks, Salah Abdeslam, said that they will no longer defend him, speaking during a TV interview on Wednesday.

A French court charged Paris attacks suspect Salah Abdeslam over his role in the November 2015 carnage that left 130 dead, just hours after his extradition from Belgium.