Belgian police on Thursday detained three people over a suspected plot to attack the country’s politicians including Prime Minister Bart De Wever with a drone carrying explosives.

The three were taken into custody after an anti-terrorism judge ordered searches of their homes in the port city of Antwerp by police officers working with explosives sniffer dogs, federal prosecutors said in a statement.

An “improvised device” was found at the home of one of the suspects but it was not operational at the time. A bag of steel balls also was found there, while a 3D printer believed to be used to make parts for the planned attack was found at another residence.

“There are also indications that the intention was to build a drone to attach a load,” the prosecutors said.

The raids were “part of an investigation into, among other things, attempted terrorist murder and participation in the activities of a terrorist group,” they said.