The U.S. Coast Guard has rejected comments by a Chinese diplomat that its recent boardings of Chinese fishing boats in the Pacific Islands alongside local police are illegal, saying the joint patrols are at the behest of Pacific nations to protect coastal fisheries.

Last month six Chinese fishing boats were found to be violating Vanuatu's fisheries law after being inspected by local police who were on board the first U.S. Coast Guard boat to patrol the waters of the Pacific Islands nation.

In a letter circulated by the Chinese Embassy on Friday, China's Ambassador to New Zealand Wang Xiaolong said the use of "shiprider" agreements between the U.S. and Vanuatu, Kiribati and Papua New Guinea to "carry out law enforcement activities against China's fishing vessels" was a violation of international law.