The three said last November's independence referendum showed a majority of New Caledonians wanted to stay French.
They said they would therefore oppose any attempt to dispossess the country of part of its land and wealth.
FLNKS leader Daniel Goa says unlike the people of Vanuatu, the Kanaks had no cultural links to the two islands.
He says it was more of a case of France wanting to keep its maritime area, being driven by economic interest.
According to a New Caledonian public law professor specialising in territorial issue, the two countries were likely to keep their territorial dispute out of the courts.