Five people accused of planning to bomb the mayor of Leeuwarden and the summer Nato summit in The Hague have been remanded in custody at a pro forma hearing.

The five, in their 60s and 70s, are all said to be from the radical wing of a group known as “sovereign citizens” – people who do not recognise the rule of law and refuse to pay taxes, fines or healthcare premiums.

The AIVD security service, police and anti-terrorism unit NCTV said their number has grown to some tens of thousands in the last few years. Around 100 supporters turned up at court in Leeuwarden for Wednesday’s hearing.

In total, eight people were arrested in a string of raids on June 11, most of them in Friesland. “These suspects are part of a small extremist group which is prepared to use deadly force,” the public prosecutor said in court.

Raids on their homes turned up a number of weapons and five bottles filled with castor beans, which can be used to make the deadly poison ricin. One of the five had instructions on how to do this, the public prosecutor said.

Three other suspects were released earlier. The main trial will take place in December.