"I have a letter for you from Vice-Admiral Philippe Euverte [of the French Maritime Forces of the Pacific Zone]. We will give this letter to all skippers arriving near Mururoa and Fangatuafua. This letter advises them what they can do and what they cannot," Lieutenant Yves Peant told the captain of the Tui.
A French cabinet minister, meanwhile, said that the French Navy would escort away any intruders in an exclusion zone around its South Pacific nuclear test site, which he likened to a private bathroom.
"The 12-mile zone is a bit as if you were in your bathroom and you said: 'I'm taking my bath and I don't want anyone to come in'. You wouldn't be happy if somebody did. It's the same for us," said the Minister for Overseas Territories, Jean-Jacques de Peretti.
Tui, an unarmed naval research vessel, is to monitor the safety of a protest fleet, which is likely to include about 25 craft, and which will demonstrate at France's South Pacific nuclear test sites.
Within hours of arriving outside the French exclusion zone, the Tui's captain, Lieutenant- Commander John Campbell, was radioed by the French. Three officers from the French patrol boat Gracieuse delivered the letter from Admiral Euverte. The letter said the French Navy respected protesters' rights, but warned that they should respect French sovereignty of the atoll.
"I am quite determined to enforce the law and carry out the mission I hold to safeguard the security of the testing sites", the admiral said in the letter.
"I assure you that I will always act as a sailor should you encounter difficulties and that I would not hesitate to lend you assistance if necessary," the letter said. Lieutenant Peant said the French wanted to have regular contact with the Tui.
In New Zealand, a Greenpeace spokesman, Michael Szabo, said the government had missed a "golden opportunity" to deliver an official protest letter to the French government.
He said it was inappropriate for the Tui, which "the government has sent ... to represent the views of New Zealanders" to "exchange niceties" with the French Navy without protesting against France's nuclear-testing programme.
Greenpeace's flagship, Rainbow Warrior II, left Papeete harbour on Thursday to join the "peace flotilla" protesting against Paris's decision to carry out up to eight nuclear tests at Mururoa and Fangatuafua from 1 September.