Brussels will remain at the highest possible alert level, with schools and metros closed over a “serious and imminent” security threat similar to the Paris attacks, the Belgian premier says.

“The threat is considered serious and imminent,” Prime Minister Charles Michel said on Sunday, a day after the authorities raised the alert level from three to four in the city that also hosts EU and NATO headquarters.

The city’s metro system will stay closed and all schools will be shut on Monday, he said after a meeting of the national security council to review the situation.

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A tense Brussels was locked down for a second day on Sunday with armed police and troops patrolling near deserted streets amid fears jihadists planned a repeat of the Paris attacks which left 130 people dead on November 13.

Michel made no direct mention of the manhunt underway for several suspects linked to the attack, including Salah Abdeslam who managed to slip past French security forces after the carnage in Paris.

Salah’s brother, Brahim, died when be blew himself up outside a bar as others attacked restaurants, a rock concert and the national stadium.

“What we fear are similar attacks, with several individuals in several places,” Michel told reporters.

“We are very aware that this situation is very difficult for everyone … we want to thank everyone for their efforts and everyone must remain vigilant,” he said.

“We are doing everything possible to return to normal life.”

The Prime Minister said officials would review the situation again on Monday, given the disruption expected in Brussels, which is a diplomatic hub as home to the European Union, NATO and a host of major political and business groups.

Michel said the rest of the country would remain on security alert level three, meaning an attack is considered possible and the threat credible.