SYDNEY, Australia — The Pacific Islands’ most important regional body is on the brink of collapse after a dispute over the election of a new leader led the nation of Palau to abandon the organization and announce the withdrawal of its embassy from Fiji.

Other Micronesian countries may follow Palau out of the group, the Pacific Islands Forum, which could hinder momentum on addressing climate change. The forum has long been the region’s megaphone, shouting for action on the world stage as those who live on hundreds of islands are inundated by rising seas and pummeled by more catastrophic storms.

“They’ve said in the past that the relationship in the Pacific is unique — it’s like a family,” said Jonathan Pryke, the director of the Pacific Islands Program at the Lowy Institute, an independent think tank in Sydney. “To have a family member leave altogether, it’s just a very bad sign.”

The forum was founded in 1971 as a representative body for the South Pacific, then expanded in 1999 to include the North Pacific, and divisions within the 18-nation organization (now 17 and shrinking) are not uncommon. Fiji was suspended from the group after a coup in 2009, returning in 2015. Six years ago, a dispute about who would lead the group as its secretary-general was resolved only after a walk and a long talk among a handful of influential leaders.

But this year, because of the pandemic, that was not possible. Covid kept the Pacific family apart: The annual forum was conducted over Zoom, and the dozens of in-person meetings that usually precede the gathering did not happen.

Mr. Pryke said that lack of connection seemed to have contributed to the explosion of long-simmering frustrations.

In general, the countries of Micronesia in the North Pacific — with smaller populations and economies — have complained of being sidelined by the larger countries to the south, including Fiji, New Zealand and Australia.

To help manage that, the forum developed a tradition of rotating the secretary-general position among leaders from Melanesia, Micronesia and Polynesia.

This week, that protocol broke down into a heated free-for-all.

A flurry of candidates emerged in early votes, and Thursday’s final election elevated a former prime minister of the Cook Islands, Henry Puna, to the role of secretary-general. In simple terms, it was Micronesia’s turn, but its candidate, Gerald Zackios, the Marshall Islands’ ambassador to the United States, lost the final tally by one vote.

Publicly, the forum said its decision had been driven by strong support for Mr. Puna.

Surangel Whipps Jr., Palau’s president, described the result as an act of disrespect.

“The process regarding the appointment of the secretary-general has clearly indicated to the Republic of Palau that unity, regionalism and the ‘Pacific Way’ no longer guide the forum,” he said.

Mr. Pryke at the Lowy Institute called the absence of consensus “a step backward” for the group, at a time when unity is especially important.

“The Pacific is facing major existential crises, the foremost of which is climate change,” he said. “They have been vocal advocates worldwide, far above their size and stature, and it’s largely because of the unity you see in the Pacific — which appears to be rapidly unwinding.”