An investigation into the Nov. 13 attacks in Paris widened on Tuesday when French prosecutors said a man who provided lodging to the suspected ringleader must have known of a militant plot, and Belgium issued a warrant for a new suspect.

Painting a chilling picture of ringleader Abdelhamid Abaaoud, the Paris prosecutor 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, in which 130 people were killed, prompted France to declare a national state of emergency and to step up air strikes in Syria on Islamic State, the militant group that has claimed responsibility.

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

At a joint news conference, Hollande said he and 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 capital's business district. Reuters exclusively reported the plot to attack the district of La Defense on Nov. 18.

Molins said he had put under formal investigation a Frenchman who had provided lodging for Abaaoud and his associates at the apartment in the suburb of St. Denis.

"Jawad Bendaoud himself welcomed the terrorists on Nov. 17 towards 10:45 p.m. He could not have been in any doubt ... that he was taking part in a terrorist organisation," Molins told a news conference.

Bendaoud said that before he was detained by police last Wednesday 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 Aitboulahcen, a woman believed to be his cousin, and an as yet unidentified third person.