Belgium on high alert, warns of 'serious and imminent threat' to Brussels

Source: CNN

This will not be a normal Saturday in Brussels. The Belgian capital is on the country's highest terrorism alert level.

The warning, from the Crisis Centre of the Belgian Interior Ministry, cites "a serious and imminent threat that requires taking specific security measures as well as specific recommendations for the population."

It advises the public to avoid places where large groups gather -- such as concerts, sporting events, airports and train stations -- and comply with security checks.

The city's underground metro service will not be running on Saturday and other public transit will be operating on a limited schedule, the ministry said.

Outside of Brussels, the rest of the nation will maintain its current terrorism level.

 Why now?

If people take the alert seriously, Brussels will be "shut down tomorrow," CNN terrorism analyst Paul Cruickshank said.

"It suggests they have something specific and credible at the intelligence front pointing them in the direction that there may be a terrorist plot in the works," he said. "It also suggests they don't have a handle on it, that they don't know where these plotters are or where they're coming from."

The increase in the alert level for Brussels comes as authorities investigating last week's terrorist attacks in Paris conduct raids in Belgium. They are working to identify and take down the network of terrorists behind the carnage.

The U.S. State Department advised Americans there to be cautious.