BRUSSELS — Belgian security forces made more than a dozen arrests in a series of raids across the capital on Sunday night as they hunted down suspected Islamic State militants, but said sweeping security measures would be kept in place as the major suspect from the Paris attacks remained at large.

Prosecutors said 16 people had been apprehended during 22 house raids amid fears that allies of the Islamic State may be planning a similar attack in Brussels. Police opened fire during one raid after a vehicle sped at them.

Belgian officials decided on Sunday to extend a partial lockdown of the city through Monday, keeping the capital on its maximum terrorism alert level. Besides the metro, schools will also be shut.

Prime Minister Charles Michel said that authorities had received “additional information” on Sunday that had led to his decision to enforce the extraordinary measures.

“We fear an attack like the attack in Paris,” he said in a news conference. “Meaning several individuals conducting an attack in Brussels, possibly in several places at the same time.”

The highly unusual measures in the Belgian capital underscore the fear gripping Europe a little more than a week after the coordinated assaults in Paris, which killed 130 people and injured more than 350 and brought into focus the Islamic State’s ability to strike the West directly.

Not since Boston came to a near standstill after the Boston Marathon bombing in 2013 has the life of a major Western city been brought to a halt this way by the fear of terrorism.

Police in France released a photo Sunday night of an unidentified attacker, one of three who blew themselves up at Stade de France on Nov. 13. The man is suspected of having traveled on a fake Syrian passport through Greece on Oct. 3. Police are asking people who might recognize the face in the photo to contact them.

The possibility that one or more of the Paris attackers may have arrived among the waves of refugees from the Middle East has intensified debate in the United States as well as Europe over their welcome in the West.

Belgian authorities say they have acted in response to a plot that included shopping centers and public transportation as soft targets for a possible large-scale attack. The government has warned residents to avoid crowded locations.

As raids were carried out on Sunday night, streets were shut down in central Brussels, and police urged residents not to post details of the operations on social media. Nineteen raids were carried out in the Brussels area and three more in Charleroi, around 46 miles south.

Grand Place, the central square of the Belgian capital, was evacuated on Sunday night because of a “police operation,” national broadcaster RTBF television reported. Guests in nearby hotels were told to stay indoors.

Belgian Justice Minister Koen Geens apologized on Sunday for the shutdown of the subway system, which continues as authorities extend their hunt for suspects.

“We are doing all we can to make that possible with the capacity we have now. We don’t want to paralyze Brussels economically, but we need time to arrange all this,” Geens said.

Belgian officials are casting a wide net for those involved in the Paris attacks and others who may be preparing to strike in Belgium. A primary target is Salah Abdeslam, a 26-year-old French national who is the subject of a manhunt across Europe. Abdeslam, who was identified as one of at least nine suspected attackers, is believed to have made his way to Belgium after the attacks.

Abdeslam was not among those arrested on Sunday night, Belgian prosecutors said. In recent days, police raids in Molenbeek, the largely immigrant area of Brussels that several of the Paris attackers called home, and in other neighborhoods had uncovered explosives and weapons, but none were recovered on Sunday, prosecutors said.

During a raid near a snack bar in Molenbeek, however, police fired two shots after a car rushed at them. The car escaped but was later stopped by police, and the wounded driver was arrested.

Most of the identified attackers are French and Belgian nationals who became radicalized in Europe. Some are known to have traveled to Syria to fight with the Islamic State.

Belgian Interior Minister Jan Jambon told Flemish national television that authorities were still looking for members of the suspected militant cell linked to a Brussels plot or their accomplices.

“It involves several suspects, and that is why we have put in place such exceptional measures,” Jambon said.

The Belgian government faces a difficult task in managing what it sees as an acute threat while also minimizing the disruption and anxiety caused by security measures.

“We are following the situation minute by minute. There is no reason to hide that,” Jambon said. “There is a real threat, but we are doing everything possible day and night to face up to this situation.”

On Friday, a Belgian citizen was charged as an accomplice in connection with the Paris attacks and participation in a terrorist group. His name has not been released.

Investigators have extended their search for Abdeslam, who was last seen the day after the attack in a car pulled over by police near the Belgian border.

According to a lawyer for one of two Belgian men who were with Abdeslam in the car at the time and who have now been detained, Abdeslam’s companion described him as extremely angry and possibly “ready to blow himself up.”

Abdeslam is the only remaining operative in the core group of Nov. 13 attackers thought to be alive. But officials think there may have been a wider group linked to the attacks.

In France, normal life has gradually returned to the streets of Paris more than a week after the attacks, even as the government of President François Hollande moves forward with plans to tighten security, surveillance and border controls. Police have extended a ban on public gatherings until Nov. 30.

On Friday, French lawmakers approved a three-month extension to a state of emergency decreed by Hollande after the attack. Hollande has also proposed changes to France’s constitution.

Hollande will discuss the campaign against the Islamic State and Europe’s own safety this week in a series of high-level meetings. Monday, Hollande will receive British Prime Minister David Cameron at the Elysée palace. Later in the week, the French leader is due to hold talks with President Obama, German Chancellor Angela Merkel and Russian President Vladimir Putin.

France is promising to intensify its military response to the Islamic State, which is dug in across Iraq and Syria despite a year of U.S. and allied airstrikes. On Sunday, French Defense Minister Jean-Yves Le Drian said the aircraft carrier Charles de Gaulle had arrived in the eastern Mediterranean and would be ready to launch combat flights Monday against the Islamic State. France began airstrikes in Syria in September.

“If we let Daesh flourish in Syria and Iraq, we are allowing Daesh to organize against us,” Le Drian told Europe1 radio. Daesh is another name for the Islamic State.

U.S. and French military goals in the campaign against the group are complicated by the fact that Russia is now also conducting airstrikes in Syria, mostly in support of President Bashar al-Assad, who Western nations say must step down.

Gen. Pierre de Villiers, chief of France’s defense staff, said in an interview published Sunday with French newspaper Le Journal du Dimanche that a barrage of airstrikes launched by French fighter jets since the attack had “seriously hurt” the Islamic State.

The Islamic State has released a series of new videos saying that Western war planes had hit a medicine depot and other civilian sites.

In the slickly produced videos, Islamic State fighters praised the Paris attacks and threatened further violence against France and on the United States. One videos shows a simulation of the Eiffel Tower toppling to the ground.

“Haven’t you understood yet?” one masked militant, speaking in French, asks in another video. “Today the Muslims are not the same as they were before. . . . Now Muslims are respected.”

In another video, a militant says the group has “lots of candidates” for suicide operations.