It's the latest reaction to a French naval mission the the small uninhabited islands in January, when officers landed and painted the French flag on a rock.
In the the most scathing comments yet on the dispute, Mr Salwai said France had also disrespected Vanuatu's culture.
In a letter to French Prime President Emmanuel Macron, he said the government's priority was to see the return of Matthew and Hunter.
In comments reported by the Vanuatu Daily Post, Mr Salwai added that Vanuatu wanted a "friendly solution" to boundary issues with France.
