Belgian authorities raised the terror alert in the region of Brussels to the highest possible level fearing a “very serious” and “imminent” threat.

The underground will remain closed until at least Sunday and the citizens have been warned to avoid places of mass gatherings, including shopping centers and concerts.

The warning for the rest of the country remains at a lower, but still serious level, the BBC informs.

Some of the suspected perpetrators of last week's attacks in Paris, which claimed the lives of 130 people and left hundreds injured, were from Brussels.

One of them, Salah Abdeslam, is believed to have returned to Belgium in the aftermath of the attacks. So far, the Belgian authorities have accused three people of involvement in the attacks.

The Brussels suburb of Molenbeek, which is known as a breeding ground for jihadists, was the subject of a large-scale manhunt for suspected perpetrators of the Paris attacks in the beginning of the week.

There were even reports that the key suspect Abdeslam was detained, but these were later dismissed.

Security concerns led to the cancellation of the friendly football match between Belgium and Spain, which had been scheduled to take place at the King Baudouin stadium in Brussels on Tuesday.

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