The Brussels-based Islamic State jihadists behind the Paris attacks planned a fresh strike in France but targeted the Belgian capital instead as police closed in, the federal prosecutor said on Sunday.

The prosecutor also announced that the so-called "man in the hat" Mohamed Abrini had been charged with "terrorist murders" over the attacks in Brussels last month.

Suicide bombers claimed 32 lives when they blew themselves up at Brussels airport and at a metro station on March 22 but left a trail for police leading directly to the November Paris attacks which killed 130 people.

"Numerous elements in the investigation have shown that the terrorist group initially had the intention to strike in France again," the Belgian federal prosecutor's office said in a statement.

"Surprised by the speed of the progress in the ongoing investigation, they urgently took the decision to strike in Brussels."

The prosecutor gave no further details but the Brussels onslaught followed the March 18 arrest of top Paris attacks suspect Salah Abdeslam after four months on the run.

The prosecutor also gave no details of the planned attack in France but late last month, French police arrested Reda Kriket near Paris, finding weapons and explosives in a flat he had used to suggest he was planning an attack of "extreme violence."

Belgium has arrested two suspects, identified as Abderrahmane A. and Rabah M, in connection with the Kriket case and on Thursday both were remanded in custody, along with three other suspects held in connection with the November Paris attacks.

Shortly after Kriket's arrest, French prosecutor Francois Molins had said that "while no specific target has been identified, nonetheless everything leads us to believe that the discovery of this cache (of weapons) has allowed us to prevent an action of extreme violence by a terrorist network".

'Man in the hat'  

In Sunday's statement, the Belgian prosecutor said Abrini, the man seen in CCTV footage with the two suicide bombers at Brussels airport, had been charged with "terrorist murders".

"The investigating judge specialised in terrorism cases has put Mohamed Abrini in detention in connection with the investigation into the Brussels and Zaventem (airport) attacks," the statement said.

"He is charged with participation in the activities of a terrorist group, terrorist murders and attempts to commit terrorist murders."

On Saturday, the judge leading the Belgian investigation into the Paris carnage laid the same charges against Abrini, who was arrested on Friday.

The 31-year-old Belgian of Moroccan origin confessed to being "the man in the hat" who calmly walked away from the devastated departure hall, the prosecutor said on Saturday.

He then returned on foot to central Brussels, discarding his hat and coat on the way before disappearing into thin air as the police launched a fresh appeal to the public for help.

Authorities criticised  

Abrini was a long-time petty criminal who grew up with Abdeslam in Belgium's troubled Molenbeek area, home to several other suspects who all share a similar story of getting on the wrong side of the law and becoming radicalised.

The Belgian authorities have faced intense criticism over their handling of the Brussels attacks and the investigation, especially as it has emerged that many of the suspects were known to the police.

Critics say the government has not done enough to prevent extremists targeting Muslim youth in areas such as Molenbeek, with Belgium proportionately the biggest source of foreign fighters going to join the Islamic State group in Syria.

Abdeslam, whose brother Brahim blew himself up in Paris, was seen driving to the French capital with Abrini shortly before the attacks but he apparently balked at the same mission and fled back to Brussels.

Police finally arrested him not far from the family home in Molenbeek after apparently stumbling upon another jihadist safe house in the Forest area of the city.

There has been much recrimination in Belgium about how he and the others were able to remain free for so long, with two ministers offering to resign.

Buoyed by Abdeslam's arrest, the police launched an increasing series of raids, mainly in Brussels, resulting in more detentions as they closed the net.

Abdeslam is now awaiting extradition to France.

"That is justice... he who does something must pay the price," Abdeslam's father, who has lived in Belgium for 40 years, told French radio Europe 1 on Tuesday.

"I hope everyone will speak now... we were there, we were happy, we had enough, we went out, had fun but now, we cannot even leave our house," he said.