Three prison workers at separate jails have been targeted by explosions at their homes in the space of three weeks, in a development described as “unacceptable“ by prison service director Jannine van den Berg.

One staff member at Krimpen aan den IJssel prison was injured when a device went off at his home on August 20, while two other blasts in August damaged the homes of workers at Zaanstad detention centre and Heerhugowaard prison.

In another incident reported in the prison service’s monthly log, a prison worker needed hospital treatment after being assaulted with a baseball bat outside the jail in an apparently unprovoked attack.

Van den Berg said in a LinkedIn post headed “hands off our people” that it was “unacceptable” for prison staff to be attacked in their own homes.

“A society in which colleagues are intimidated in their private lives for doing their job is not a society we should accept,” she said.

Police investigations into all four incidents are ongoing.