How serious was this potential attack?  Serious enough that Belgian law enforcement says that one suspected al-Qaeda terrorist had already said goodbye to his family.  Police rounded up fourteen suspects in 16 raids, and they think the European Union summit could have been the target (via Power Line):

The arrests were made during 16 raids in Brussels, as European Union leaders gathered for a summit there, and one in Liege.

“We don’t know where the suicide attack was to take place,” federal prosecutor Johan Delmulle said.

“It could have been an operation in Pakistan or Afghanistan, but it can’t be ruled out that Belgium or Europe could have been the target.”

One of the suspects had “received the green light to carry out an operation from which he was not expected to come back,” Mr Delmulle quoted investigators as saying.

The man “had said goodbye to his loved ones, because he wanted to enter paradise with a clear conscience”, he added.

“This information, linked to the fact that a European summit is getting under way at this moment in Brussels, left us no choice but to take action today.”

This particular cell in Belgium has participated in training fighters who later went to the Pakistan-Afghanistan border to battle NATO.  The arrests capped off a year-long investigation into the group’s activities, and it looks like the raids intended to head off an attack that may have just been days or hours away.

More to follow as details emerge.