Belgian police during raids in Brussels on Tuesday linked to probes into last year’s Paris attacks. (Thierry Monasse/AP)

Belgium’s prime minister said Wednesday that raids against suspected Islamist militants will “almost certainly continue” following police sweeps in Brussels in which a gunman with apparent Islamic State links was killed.

The announcement came as French police arrested four people early Wednesday morning in Paris and its suburbs, one of whom had been under house arrest on suspicion of being in contact with operatives of the Islamic State militant group.

“The level of threat remains high,” said French President François Hollande. “We saw it again in these last few hours in Brussels. And we see it with these arrests. We should have the greatest vigilance possible.”

Few details are known about the arrests in France, but Interior Minister Bernard Cazeneuve said the three men and one woman — all French-born and ages 21 to 30 — were taken into custody for questioning.

“We had, regarding one individual detained, reports that he may engage in violent acts in France,” Cazeneuve said. “This individual could be linked to individuals in Syria belonging to the Islamic State.”

Armed Belgian police lock down a section of Brussels and tell residents to stay indoors as they hunt for a fugitive gunman linked in the investigation into the deadly Paris attacks in November. (Reuters)

A police search of their apartments found an unused Kalashnikov cartridge, USB cards and SIM cards, according to the Associated Press.

Five months after the Nov. 13 attacks in Paris, tensions remain high in the French capital, as well as in the Belgian capital, where officials believe the coordinated Paris assault was largely planned.

The prospect of more police action in Brussels suggests that the Belgian capital remains a central focus of investigations into the November attacks — which killed at least 130 people — and wider confrontations against suspected militant networks based in Europe.

Eric Van der Sijpt, a spokesman for Belgium’s federal prosecutor, said Belgian authorities have carried out more than 100 house searches since November and arrested 58 people thought to have been involved in the attacks. At least 10 people are still being held.

On Tuesday, a joint French-Belgian operation linked to the Paris investigation moved into a Brussels neighborhood, touching off clashes that left one suspect dead. Authorities identified him as Mohamed Belkaid, a 35-year-old Algerian.

According to Van der Sijpt, Belkaid was found in an apartment with a Kalashnikov rifle, ammunition and others items, including an Islamic State flag. Belkaid was in the country illegally, Van der Sijpt added, but he gave no further details.

Two other people in the apartment apparently fled during the raids in the area, known as Forest.

“Police operations [and] investigations are underway and will most certainly continue in the hours and the days ahead,” Prime Minister Charles Michel said before a meeting of Belgium’s National Security Council. “The threat remains present.”

Another suspect was apprehended Wednesday, Belgian media reported.

One of the key suspects in the November attacks, the 26-year-old one-time Brussels resident Salah Abdeslam, remains at large.

Read more:

9 young men and their paths to terror in Paris

Is it too late to solve the mess in the Middle East?

The Belgian neighborhood indelibly linked to jihad

Islamic State has increasingly hit soft targets outside of ‘caliphate’ borders