A New Zealand research ship has enraged Vanuatu's government, and possibly threatened long-running negotiations over a pair of disputed islands.
The ship, Braveheart, has been carrying a marine science team around the Matthew and Hunter islands.
The uninhabited islands have been claimed by both Vanuatu and France since 1976, when France annexed them for New Caledonia ahead of Vanuatu being granted independence.
Vanuatu's prime minister, Charlot Salwai, said that the New Zealand team had asked the government in New Caledonia if it could carry out research, but not Vanuatu.
He said the ship was in Vanuatu's waters illegally.
This year, momentum on the dispute appeared to be building, with the two sides agreeing to a proposal for boundary negotiations.
But Mr Salwai said all boundary issues should have been sorted before any agreement was made to do scientific research.
He said Vanuatu was raising the issue at the highest level with the governments of New Zealand, New Caledonia - and the United Nations.