A prosecutor on the Greek island of Lesbos has brought criminal charges against five members of international charities for allegedly trying to help migrants illegally enter Greece.

The three Spanish and two Danish nationals face a minimum five-year prison sentence if they are convicted. The suspects, who deny any wrongdoing, will appear before an investigating judge on Lesbos Saturday.

They were arrested earlier Thursday for allegedly setting off in a rescue vessel to assist a migrant boat in Turkish waters without clearance from the Greek coast guard.

Hundreds of thousands of migrants have reached Lesbos in frail boats from nearby Turkey — technically an illegal border crossing — over the past year. Many international charities are active on the island.