Belgian police carried out raids throughout the tense capital, detaining 16 people, prosecutors said early Monday. Paris fugitive Salah Abdeslam was not among those arrested, and security remained high with a terror alert for the third straight day.

Federal prosecutor Eric Van Der Sypt said 19 raids were carried out in Molenbeek, home to many of the Paris attackers, and other boroughs of Brussels and three raids were carried out in other cities.

"We have to stress that no firearms or explosives were discovered ... during the raids," Van Der Sypt said.

One of those detained was injured when a car he was in tried to ram police during an attempted getaway, Van Der Sypt said.

The raids capped a tense day with hundreds of troops patrolling and authorities hunting for one or more suspected extremists, the Belgian government chose Sunday to keep the capital on the highest state of alert into the start of the workweek to prevent a Paris-style attack.

Citing a "serious and imminent" threat, Prime Minister Charles Michel announced that the subway, schools and universities in Brussels would be closed Monday, preventing a return to normal in the city that is also home to the European Union's main institutions.

Western leaders stepped up the rhetoric against the Islamic State group, which has claimed responsibility for the attacks in Paris that killed 130 people and wounded hundreds more; the suicide bombings in Beirut that killed 43 people and injured more than 200; and the downing of the Russian jetliner carrying 224 people in Egypt's Sinai Peninsula. All happened within the past month.

"We will not accept the idea that terrorist assaults on restaurants and theaters and hotels are the new normal, or that we are powerless to stop them," President Barack Obama said in Kuala Lumpur, Malaysia.

British Prime Minister David Cameron and French President Francois Hollande, meeting in Paris, paid a quiet visit to the Bataclan concert venue, which saw the worst of the carnage in the Nov. 13 attacks that killed 130 people.

Authorities frantically searched for Abdeslam, who is believed to have played a key role and who crossed into Belgium the day after the attacks.

Several of the Paris attackers had lived in Brussels, including Abdelhamid Abaaoud, the plot's orchestrator who was killed Wednesday in a standoff with French police. Police issued a new appeal to identify the third attacker who was killed in the assault at the national stadium. They posted a photo of the man on Twitter, asking the public for information that would help identify him.

France has intensified its aerial bombing in Syria and Le Drian said the aircraft carrier Charles de Gaulle, which has been sent to the Mediterranean to help combat IS militants in Syria, will be "operational" from Monday and "ready to act."

France has extended a state of emergency, which allows police raids, searches and house arrest without permission from a judge, for three months. On Saturday, it also extended a ban on demonstrations and other gatherings through Nov. 30, when a U.N. climate conference with more than 100 heads of state is scheduled to start.

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Lori Hinnant contributed from Paris.