Belgian Prime Minister Charles Michel has announced a series of operational measures to be implemented in Brussels following the decision to raise the alert level, Le Soir reports.

The measures include cutting the number of big events, tighter security on the public transport system, especially on the metro, boosting the number of police and soldiers, especially in Brussels, and the setting up of a hotline (1771) for members of the public to call in emergency.

Until 2006, Belgium had a permissive gun law by European standards, and many weapons used in the 1990s Balkan wars easily found their way into the Belgian criminal underworld. At the same time, the Justice Ministry was hurt by austerity measures, rendering it powerless to dig into the root causes of the problem.

"It is relatively easy to get your hands on heavy arms in Brussels," said Brice De Ruyver, a professor of criminology at Ghent University, who was security adviser to the prime minister from 2000 to 2008. "That applies to terror and serious crime. That is because the illegal arms trade has been neglected far too long. And once you have a reputation, it is tough to get rid of it."

Gunmen behind last January's attacks on a Paris supermarket and the office of the Charlie Hebdo magazine were believed to have purchased weapons from Belgian arms dealers.