THE HAGUE, Netherlands — Dutch prosecutors have opened a criminal investigation into an organization that aims to support its members’ efforts to buy a deadly powder to help them take their own lives.

The plan, announced last year by an organization called Cooperative Last Will, opened a new front in the long-running debate about euthanasia and assisted suicide in the Netherlands.

Prosecutors said in a statement Wednesday they were launching their investigation “because assisting suicide is illegal” and because members of the organization were planning to place orders for the powder. Neither the group nor prosecutors have identified the powder.

In a response on its website, the organization denies wrongdoing and says its lawyers are studying the prosecutors’ announcement.

While euthanasia has been decriminalized in the Netherlands if carried out by a physician who adheres to strict conditions, assisting suicide remains illegal.