The Pacific Islands Forum plunged deeper into crisis Tuesday as four more nations vowed to leave because of a leadership dispute, upending diplomacy in a region where the United States and China are competing for influence.
Micronesian countries -- the Marshall Islands, Kiribati, Nauru, and the Federated States of Micronesia -- said they would follow Palau's decision last week and pull out of the group.
They are angry that their sub-grouping's candidate to be the Forum's next secretary-general was recently rejected in favour of former Cook Islands premier Henry Puna.
"The Micronesian presidents jointly agreed that all five nations will initiate the formal process of withdrawal from the Pacific Islands Forum," the leaders said in a joint communique issued Tuesday.
The Micronesians had argued it was their turn to fill the post under an informal arrangement that has stood for decades and claimed the snub showed the Forum was biased towards members from the South Pacific.
"The forum has lost its original intent to be a regional body," Nauru President Lionel Aingimea said in a statement.
The 18-member Forum is mostly made up of small island states along with Australia and New Zealand, and is a key element of the US allies' diplomatic efforts in the region.
It has become influential on the issue of climate change, amplifying the voice of many of the region's small island states that are threatened by rising seas and ever-more intense cyclones.
A rare split in the Forum's ranks provides a potential opening for China to boost its influence with the sparsely populated but strategically important Pacific island nations, which would alarm the United States and Australia.
New Zealand Prime Minister Jacinda Ardern said she was "saddened" by the Micronesians' decision.
Ardern said PIF protocols meant it could take up to a year for the departures to take effect and, in the meantime, New Zealand would lobby dissenting nations to remain.
"We're going to do what we can to encourage leaders to stay," she told reporters.
"The strength of the Pacific Islands Forum is its wide representation and of course we want to see that remain."
There was no immediate response from the Forum, though its chairman Kausea Natano was defiant in the wake of Palau's departure last week, saying he was "steadfast" in his support of the next secretary-general Puna.
"This was a consensus decision following an agreed process... we have upheld our principles and values as characterised through the Pacific way," he said.
Natano also insisted after last week's vote on Puna's appointment that the Micronesian leaders had withdrawn their threat to leave the Forum and the organisation remained unified.