Drone Incidents Heighten Security in Belgium
Belgium's Zaventem airport closed due to drones, affecting 3,000 passengers.
United Kingdom is deploying kit; source of drones is unknown.
Belgian Defence Minister said drones over military bases were initially their problem.
Belgium hosts NATO and EU, holds frozen Russian assets.
Possible link between drone incidents and Ukraine funding talks.
Drone incidents have caused flight suspensions in European airports.
Drones near Belgium's military base storing US nuclear weapons linked to hybrid warfare.
6 days ago