American Samoa Harbour Master, Silila Patane, has written to the Office of Tokelau Affairs about the unauthorised entry of a New Zealand research vessel which berthed at Swains Island.
Mr Patane says the vessel, the MV Echo, committed an act of aggression and violated both international and American Samoan maritime law.
When he was told of the ship's arrival he immediately ordered it to leave Swains island.
Mr Patane says he was concerned that the vessel had been in Tokelau where a measles outbreak had been reported.
He says his main concern was that the research vessel was unauthorised.
"It's a spy vessel. It has all the equipment on board for recording, depth sounding and everthing else. In Tokelau they are trying to pass it away by saying the New Zealand reserch vessel Echo was contracted by the SPREP people, but whatever they say it's not right. They think they are talking to a kid at a kindergarten."