PARIS/BRUSSELS • An investigation into the Nov 13 attacks in Paris has widened after French prosecutors said a man who provided lodging to the suspected ringleader must have known of a militant plot, and Belgium issued an arrest warrant for a new suspect.

Painting a chilling picture of ringleader Abdelhamid Abaaoud, the Paris prosecutor on Tuesday said that after dropping off the gunmen and suicide bombers at the cafes and bars where the attacks were to take place, he later returned to the scene while the killing spree was in full swing.

The coordinated attacks, which killed 130 people, prompted France to declare a national state of emergency and to step up air strikes in Syria on the militant Islamic State in Iraq and Syria (ISIS) group that has claimed responsibility.

President Francois Hollande, seeking to rally global support for the military campaign against ISIS, met US President Barack Obama at the White House on Tuesday where they agreed to scale up operations against ISIS in Syria and Iraq.

At a joint news conference, Mr Hollande said he and Mr Obama shared a "relentless determination to fight terrorism anywhere and everywhere".

In Paris, prosecutor Francois Molins said Islamist militants who died during a shootout with police on Nov 18 had been plotting an attack on the French capital's business district. Mr Molins said he had put under formal investigation a Frenchman who had provided lodging for Abaaoud and his associates at an apartment in the St-Denis suburb.

"Jawad Bendaoud himself welcomed the terrorists on Nov 17 towards 10.45pm. He could not have been in any doubt... that he was taking part in a terrorist organisation," Mr Molins told a news conference.

Bendaoud said before he was detained by police last Wednesday that he had been asked to put up two people for three days in the apartment, but had no idea one of them may have been the suspected mastermind of the Nov 13 attacks.

Abaaoud died during the police raid along with Hasna Ait Boulahcen, a woman believed to be his cousin, and an as yet unidentified third person.

French investigators are still piecing together exactly who did what when, and have launched a hunt to find Salah Abdeslam, who is suspected of being the eighth attacker mentioned by ISIS when it claimed responsibility.

Abdeslam, 26, fled to Belgium the day after the shootings and his presumed presence in Brussels was one of the factors behind a security lockdown in the city over the past few days.

Fearing an imminent Paris-style attack, Belgium has extended a maximum security alert in Brussels until next Monday. About half the stations on its metro system reopened yesterday, along with city schools, with 300 additional police officers and 200 soldiers deployed.

Belgium has been at the heart of investigations into the attacks since France said two of the suicide bombers in Paris had lived there. Five people, including two who travelled with Abdeslam back to Brussels, have been charged with terrorist offences in Belgium. Abdeslam's brother, Brahim, blew himself up.

Belgium's state prosecutor, in a statement announcing details of other people charged in the case, on Tuesday said it had issued an international arrest warrant for Mohamed Abrini, who was seen with Abdeslam two days before the attacks.

Abrini, 30, was filmed with Abdeslam at a petrol station in northern France on Nov 11 and was driving the Renault Clio later used by the attackers in Paris.

A police wanted poster describes Abrini as "dangerous and probably armed".

Tracing Abdeslam's movements since the attacks has been a main focus of the Paris investigations. An explosive belt was found dumped near the capital on Monday, close to a location where his mobile phone was detected the night after the attacks, the prosecutor said.

Mr Molins said the belt was similar to those used by the bombers during the Nov 13 attacks, although it was still not confirmed that the belt was Abdeslam's.

One theory was that Abdeslam had intended to blow himself up in the 18th district of Paris but had abandoned the plan, although it was not clear why.

REUTERS