Brussels remains under highest terror alert amid warning of 'imminent threat'

It has been nine days since a wave of ISIS attacks in Paris killed 130 people . French authorities have said the Paris attacks were organized in Belgium.

According to Belgian federal prosecutor Frederic Van Leeuw, authorities carried out some 20 searches Sunday and 16 people were arrested. No firearms or explosives were found.

Also not found: At least one man suspected of involvement the Paris violence, Salah Abdeslam , a French citizen who grew up in Belgium, remains at large. The prosecutor did not identify any of those people in custody.

Meanwhile, the French National Police posted a picture of a man it said was one of the dead Paris attackers on its official Twitter account . The photo is accompanied by an appeal to the public for information about the man, whom officials do not name.

"This individual is the third perpetrator who died in one of the attacks committed on November 13 at the Stade de France," the alert reads.

It asks the public to alert police if any information about the deceased suspect is known.

Children in France on Monday will have their bags searched at the front doors of schools, while administrators will be tasked with verifying the identities of everyone on school grounds, according to the Ministry of National Education website.

Gatherings around the front doors of schools are discouraged, the ministry said, explaining parents should drop off their kids and promptly leave and principals should designate on-campus sites where students can gather and older students can smoke. Field trips to the Paris area are canceled until next week, though trips within the Paris region can resume, the ministry said.

And while French officials scrambled to keep citizens safe, some took safety into their own hands, to a degree: French Samaritan Croix Blanche, an association of aid workers, announced that a record number of people were signing up for lifesaving classes.

Belgium's capital will remain at the country's highest terrorism alert level, Belgian Prime Minister Charles Michel said Sunday evening. Authorities warned Friday night of a possible imminent threat to the capital which Michel said remains of the highest concern.

In Brussels, the subway remained closed, with only the city's above-ground trams and buses operating. People have been warned to avoid large gatherings.

Specific reasons for the extraordinary alert in Brussels weren't disclosed, but Michel said Saturday that authorities had reason to suspect possible attacks in more than one location.

"We are talking of a threat of several individuals with weapons and explosives, to launch acts, maybe even in several places at once," Michel said, evoking chilling similarities with the Paris attacks that hit restaurants, a rock concert and the area outside a sports stadium.

Michel said the authorities' main objective is to reduce the number of large events so police officers can be freed up to secure Brussels. A top-tier soccer game that was due to be played 50 miles outside the capital was canceled because of the need for police inside the city.

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