Belgium placed at highest terror level

Belgium has placed Brussels at the highest terror alert level, citing a "serious and imminent threat that requires taking specific security measures as well as specific recommendations for the population."

The announcement by the Crisis Centre of the Belgian Interior Ministry is advising the public to avoid places where large groups gather -- such as concerts, sporting events, airports and train stations -- and comply with security checks.

The increase in alert level comes as authorities investigating last week's terror attacks in Paris conduct raids in Belgium as they work to identify and take down the network of terrorists behind the carnage.