Drones have been seen flying over a Belgian military base near the Dutch border for a third night in a row, according to the country's defence minister said. A helicopter was deployed to the Kleine-Brogel base after drones were spotted - they then flew off towards the Netherlands, national broadcaster VRT reported. Defence Minister Theo Francken said an investigation was under way, calling it a clear mission targeting Kleine Broge. Francken told Belgian radio on Monday that it looked like an espionage operation, but said he would not speculate on who could be behind it. I have some ideas, but I'm going to be cautious, he added.