PARIS — Belgium’s capital was under the country’s highest terror alert level Saturday — with Brussels’ subway service suspended and people warned to avoid gatherings — as authorities warned of a possible imminent threat a week after deadly attacks in Paris.
Specific reasons for Friday night’s alert weren’t released, but as news of the heightened security measures spread, so did information about four new arrests tied to the Paris probe — one in Brussels’ Molenbeek suburb, and three in Turkey.
The Belgian Interior Ministry’s crisis center cited only “a serious and imminent threat” when it announced Brussels’ terror alert level was rising to 4, the country’s highest.
Brussels’ subway system will be closed until at least Sunday afternoon, when the threat will be re-evaluated, Belgian Prime Minister Charles Michel said Saturday.
The government advised the public to avoid places in the capital where large groups gather — such as concerts, sporting events, airports and train stations — and comply with security checks. Michel said authorities’ main objective is to reduce the number of large events to free up police officers to secure Brussels.
Brussels’ streets, while not empty, were relatively sparse on Saturday afternoon. Armed security officers wearing camouflage could be seen on the streets and in front of metro stations.
Outside of Brussels, the nation will maintain its current terrorism level.
Arrests in Molenbeek, Turkey
Meanwhile, news spread of Friday arrests in Belgium and Turkey that authorities said were linked to investigations into last week’s attacks that killed 130 people in the Paris area.
In the Brussels suburb of Molenbeek, police arrested one person Friday and searched a home, Belgium’s federal prosecutor’s office said. A few weapons were found, but no explosives, the office said. No further information about the arrest or the suspect was released.
Authorities say Molenbeek, an area with a history of links to terror plots, was a home base to some of the Paris attackers, including two brothers. Those brothers were Ibrahim Abdeslam, who died in the attacks, and Salah Abdeslam, who police say is on the loose.
Also Friday, Turkish authorities said they arrested three people with suspected ties to ISIS.
It identified one of the suspects as Ahmet Dahmani, 26, a Belgian national of Moroccan descent, who allegedly scouted target sites for the Paris attacks. He was arrested at a hotel in Antalya, CNN Turk reported.
Two other suspects, Syrian nationals Ahmet Tahir, 29, and Mohammed Verd, 23, were arrested after they traveled from Syria to meet Dahmani, authorities said. The two were going to transport him to Syria, authorities said.
Brussels alert: Why now?
The increase in the alert level for Brussels comes after authorities conducted a number of raids in the capital and across the country after the attacks in France, Belgium’s southern neighbor. They are working to identify and take down the network of terrorists behind the carnage.
If people take the new alert seriously, Brussels will effectively be “shut down” Saturday, CNN terrorism analyst Paul Cruickshank said.
“It suggests they have something specific and credible at the intelligence front pointing them in the direction that there may be a terrorist plot in the works,” he said. “It also suggests they don’t have a handle on it, that they don’t know where these plotters are or where they’re coming from.”
The U.S. State Department advised Americans there to be cautious.
Salah Abdeslam on the run
Salah Abdeslam, 26, is the subject of an international search warrant. He was last seen on the night of the November 13 Paris attacks, driving toward the Belgian border. Police stopped and questioned him a few hours after the attacks, but let him go, not knowing that he was allegedly involved. His whereabouts are unknown.
ISIS has claimed responsibility for the Paris attacks.
Abdeslam is one of two brothers allegedly involved in last week’s coordinated attacks at the Bataclan concert hall, outside the French national soccer stadium and at restaurants in Paris. Although he is a French national, he was born in Belgium.
That is one of several connections between the Paris attacks and Belgium, a country seen as fertile ground for jihadist recruiters. Members of a suspected terrorist cell waged a deadly gun battle in January with police in Belgium.
The country was also home to Abdelhamid Abaaoud, who is suspected of having been the ringleader of the Paris attacks. Abaaoud was killed Wednesday during a police raid in the Saint-Denis neighborhood outside Paris.
French Interior Minister Bernard Cazeneuve said Abaaoud “played a decisive role” in the Paris attacks and played a part in four of six terrorist attacks foiled since spring, with one alleged jihadist claiming Abaaoud had trained him personally.
Abaaoud was once allegedly involved in gangs in Molenbeek. Because of Molenbeek’s links to terrorist plots, Belgian special operations forces conducted raids there Monday.
On Thursday, Belgian authorities detained nine people in raids across the country, the federal prosecutor’s office said. Seven of them were questioned after six raids around Brussels related to Bilal Hadfi, one of the November 13 Paris attackers. Hadfi, authorities say, blew himself up outside the Stade de France just outside Paris during a France-Germany soccer game.
France’s state of emergency
On Friday, the French Parliament extended the country’s state of emergency by three months. President Francois Hollande had declared the emergency after the the Paris attacks; it gives police additional powers to stop and search people, enforce house arrests and prohibit mass gatherings, among other things.
The country’s authorities have used it to detain dozens of people, put more than 100 others under house arrest and seize an array of weapons. France’s constitutional council still has to review the bill, but no problems are expected.
Since the attacks last Friday, 164 people considered dangerous have been placed under house arrest, according to Prime Minister Manuel Valls.
Woman didn’t kill herself
Also Friday, the Paris prosecutor’s office announced that Hasna Ait Boulahcen, the woman found dead after Wednesday’s police raid in Saint-Denis, did not blow herself up in that raid as previously thought.
Instead, a man wearing a suicide device was the one that detonated, the prosecutor’s office told CNN.
Boulahcen, 26, was a relative of Abaaoud, official sources in France told CNN.
Wider counterterrorism efforts
The U.N. Security Council on Friday unanimously adopted a resolution offered by France that is intended to gather international support for counterterrorism efforts, specifically aimed at ISIS.
The resolution calls on member states to take all necessary measures in compliance with international law to “redouble and coordinate their efforts.
Hollande said he would appeal to world leaders to form a wider coalition to go after ISIS, including in meetings next week with U.S. President Barack Obama and Russian President Vladimir Putin.
TM & © 2015 Cable News Network, Inc., a Time Warner Company. All rights reserved.