More than two dozen suspicious packages have found their way to local courthouses in Canada in recent weeks, sparking an international investigation, according to CBC News. Courthouses from Nova Scotia to the Northwest Territories have received the mysterious parcels, many of which carry Hong Kong postmarks. The campaign has largely targeted individual court officials in smaller towns.

Canadian police have released little information about their ongoing investigation. Police who tested packages sent to court buildings in Manitoba said they did not detect any dangerous chemicals, but revealed nothing about the packages’ contents.

Last month, four front-counter workers in a provincial Nova Scotia courthouse sought treatment at a local hospital for nausea, dizziness and burning in the throat after receiving an envelope from Hong Kong. They were all later released.

The spate of mystery packages has prompted numerous evacuations and produced a climate of unease across Canada. Authorities have warned courthouses to remain vigilant, but it remains unclear whether the campaign represents a credible threat or simply a bizarre scare tactic.

The Canadian postal service has begun screening and confiscating suspicious parcels. Last week, it intercepted three packages sent from Hong Kong and turned them over to a hazardous-materials team.

Authorities in Hong Kong have not commented on the packages or ongoing investigation. Both Hong Kong and Canada have stepped up anti-terrorist programs in recent months. There have been no indications as to whether a single person or a group is responsible.

The most recent string of packages turned up in three provincial courthouses across Saskatchewan. They were all tested by police and found to contain no hazardous materials.