The Brussels metro and schools reopened on Wednesday as the Belgian capital edged back to normal after a four-day security lockdown but the hunt went on for militants police fear may mount a Paris-style mass attack.

Troops and armoured vehicles outside reopened underground stations -- about half of the network remains closed -- and police outside schools provided a reminder of the threat the government said was so imminent that it raised its alert level on Saturday in Brussels to the maximum, where it remains.

There was less evidence of the raids and searches that have been carried out periodically in the city since two suicide bombers from Brussels blew themselves up on Nov. 13 during the Islamic State attack on Paris. The brother of one of them is still on the run, along with at least one suspected accomplice.

Of more than two dozen people detained in the past 12 days in Belgium, all but five have been released. Police have not reported finding substantial amounts of weaponry which the government says it fears a local jihadist cell could be about to use in a rerun of the violence in France that killed 130 people.

"There are maybe 10 or more people in Belgium, maybe in the neighbouring countries, present in the territory to organise some terrorist attacks," Foreign Minister Didier Reynders, speaking English, told ABC television. Aides later said the figure was based on an assumption of how many people would have to be involved to mount attacks like those in Paris.

Sister newspapers L'Echo and De Tijd quoted unidentified sources saying security operations on Sunday had foiled a major attack in Brussels. Officials declined comment and judicial sources told public broadcaster RTBF that Sunday's raids, during which 16 people were detained, were not intended to thwart attacks but rather to "give the hornets' nest a good kick".

CHARGES

Of five people held in Brussels on terrorism charges, two admit driving Salah Abdeslam, brother of suicide bomber Brahim Abdeslam, back from Paris to Brussels -- a six-hour round trip -- just after the attacks but deny any knowledge of the plot.

Salah Abdeslam, 26, is suspected of being the eighth attacker mentioned by Islamic State in its claim of responsibility. The seven others died. A suicide vest found in a Paris litter bin and mobile phone records have suggested that he may have had a change of heart.

A third man charged is accused of driving him somewhere after he reached Brussels on Nov. 14.

The fourth indictment is based on handguns and bloodstains found in the car of another man. The fifth person who has been charged has yet to be identified, but prosecutors have said that Salah Abdeslam is still at large. Police have also put out an international arrest warrant for Mohamed Abrini, 30.

Abrini was filmed driving a car with Abdeslam in northern France two days before the attacks. Like several involved, Belgian media said on Wednesday, Abrini had fought in Syria and came from the same Brussels borough as the Abdeslam brothers and Abdelhamid Abaaoud, the suspected planner killed last week.

Foreign Minister Reynders gave a number of interviews to foreign media, notably in France, to rebuff criticism Belgium had been lax in monitoring radicals. More, per head, have gone from Belgium to Syria than any other European state.

"You shouldn't always look somewhere else for reasons for what you're going through at home. We are tackling head on what is happening in some of our boroughs," he told France's Canal Plus. "When you have 130 dead in one city, it means something's gone wrong. It's a mistake, I think, to infer from that that what went wrong went wrong only abroad."

Some 200 extra soldiers guarded Brussels metro stations and an additional 300 police have been drafted in from elsewhere to protect schools in the city, causing knock-on effects.

Thursday's Europa League soccer match between Club Bruges and the Italian side Napoli was to be played behind closed doors because police are too tied up elsewhere to manage the crowd.

But the weekend's Davis Cup tennis final between Belgium and Britain is due to go ahead as planned in Ghent, west of the capital. – Reuters