This doesn’t sound very good:

More from CNN:

If people take the terror 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.”

Here’s why. “Belgium has the highest proportion of Syrian fighters as a share of its population” in all of Europe:

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