Belgium's terror alert level is to remain unchanged into next week, Prime Minister Charles Michel confirmed late Sunday.

The alert level will remain at a maximum of 4 in Brussels through Monday. Across the rest of Belgium, the alert level will stay at 3, which means "a possible and likely" threat, the prime minister announced after a meeting of the country's national security council.

The city's metro system and schools will remain closed on Monday.

Late Sunday evening, there were reports of a police operation underway in an area around the central Grand Place. Local media reports said several roads had been closed by police, and residents and tourists were told to remain indoors.

A police spokesman told Agence-France Presse that several operations were underway linked to the "terrorist threat" facing Brussels. He requested that "the media do not comment directly on the actions under way, mentioning the places for example." The public prosecutor will hold a news conference "when it is all over," he added.

Police have asked local residents not to tweet the whereabouts of security officers, as shared by the Belgian defense minister Steven Vandeput on his social media account:

No further details were immediately available.

Brussels, which is home to the European Union, European Parliament and NATO, has been in lockdown since Saturday over fears of a "specific and imminent" terrorist threat.

No further information was given about specific attacks or leads in the hunt for terror suspects linked to last week's attacks in Paris.

City on edge

The metro system was closed along with public buildings and hundreds of shops and restaurants after the terror alert was raised to the highest level of four on Saturday morning.

Streets remained empty and many of the city's top tourist attractions were deserted.

The offices of commercial TV channel VTM and the Malines-Mechelen railway station were evacuated at one point on Sunday due to bomb alerts. Both turned out to be false alarms.

Earlier on Sunday, Interior Minister Jan Jambon told Flemish broadcaster VRT that "several suspects" tied to the Paris attacks could be at large in the country.

"We have learnt that two terrorists are in Brussels territory and could commit dangerous acts," he said.

Key suspect at large

A manhunt continues for Salah Abdeslam, who is suspected of playing a key role in the mass killings in Paris. Following the attacks, he is believed to have crossed back into Belgium, where he lives.

The lawyer for Hamza Attou, one of several people arrested in Belgium last week, told French-language broadcaster RTBF that her client had dropped Abdeslam off in Brussels the day after the attacks and that he might be carrying explosives.

One of Abdeslam's brothers, Brahim, was one of the suicide bombers in the November 13 attacks.

Change of heart?

A third brother, Mohamed Abdeslam, told RTBF on Sunday that he believed Salah had changed his mind at the last moment and had not gone through with his attack.

Mohamed Abdeslam said the family wanted Salah to give himself up and would rather see him in prison than in the cemetery.

Meanwhile, a tense Belgian capital remained under tight security for a second day on Sunday with police and troops patrolling deserted streets.

Belgium is no stranger to Islamist violence. Four people were shot dead at the Brussels Jewish museum in May 2014, and in January security forces killed two suspects linked to the "Charlie Hebdo" killings in Paris in the eastern city of Verviers.

mm/cmk (AFP, dpa)