Belgium has raised its terror alert in the Brussels region to the highest level, warning of a "very serious" and "imminent" threat, reports BBC.The metro system will be closed till Sunday, and the public has been warned to avoid crowds, including shopping centres and concerts, a statement said.The warning for the rest of Belgium stays at a lower level - still serious.Brussels was home to some of the suspected Paris attackers who killed 130 people last week.One of those being sought, Salah Abdeslam, is believed to have gone back to Belgium.Turkish police say they have arrested a Belgian man of Moroccan descent on suspicion that he scouted out sites in Paris, Turkish news agencies report.The Belgian authorities have so far charged three people with involvement in the attacks, which Islamic State said it carried out.They have also recommended that large events, including football matches, be cancelled.On Friday evening, large crowds converged at the scenes of the attacks across the French capital at 21:20 (20:20 GMT) to hold vigils at the time the attacks started a week ago.Also on Friday, the UN Security Council unanimously adopted a resolution to "redouble" action against Islamic State following last week`s deadly attacks in the French capital in which 130 people died.The French-drafted document urges UN members to "take all necessary measures" in the fight against IS, which said it carried out the attacks.