Samoa police have confirmed three men have now been charged in their investigation into allegations of a plan to assassinate the prime minister.

It was revealed on Wednesday that police had uncovered a plot to kill Tuila'epa Sa'ilele Malielegaoi after being tipped off by the Lauli'i village council.

Photo: supplied / Forum Secretariat

Police said their evidence includes the use of social media both inside and outside of Samoa.

They said they take the threat very seriously and that the full weight of the government's law enforcement is being used to thoroughly investigate the matter.

Police said they are seeking help from international partners, and that further arrests could be made.

Two of the three people arrested are being held in custody.

Police said because of the seriousness of the allegations they are not releasing any other information.