The arrests were made in the northern city of Antwerp as part of an investigation into "attempted terrorist murder and participation in the activities of a terrorist group", federal prosecutor Ann Fransen told a news conference.

"Certain elements indicate that the suspects intended to carry out a jihadist-inspired terrorist attack against political figures," Fransen said.

"There are also indications that the suspects aimed to construct a drone capable of carrying a payload," she added.

The prosecutor's office declined to name the intended targets, but several Flemish media outlets reported that they included De Wever -- who was Antwerp's mayor before becoming prime minister.

"Prime Minister, Bart, all our support goes out to you and your family. Thank you to the security services," Defence Minister Theo Francken said on social media.

According to reports, police searched a residence located just a few hundred metres from De Wever's home in the city.

"During a search of one suspect's home, an improvised device -- potentially explosive but not yet operational -- was found, along with a bag containing metal pellets," Fransen said.

At the home of a second suspect, police discovered a 3D printer "believed to have been intended for manufacturing components useful in carrying out an attack", she added.

The suspects were born in 2001, 2002 and 2007.

Two of them were being questioned by federal police and were due to appear before an investigating judge on Friday.

The third suspect was released.