The four Micronesian nations are "saddened" by Kiribati's shock decision to leave the Pacific Islands Forum regional body (PIF), the Federated States of Micronesia president says.

The Micronesian Presidents' Summit (MPS) is expected to release a joint statement concerning Kiribati's departure from the regional PIF summit, in the coming days.

But, speaking to RNZ Pacific, Federated States of Micronesia president David Panuelo marked the tone of the response from the four Micronesian members at PIF - the Federated States of Micronesia, the Marshall Islands, Nauru and Palau.

"We believe that the Suva Agreement, when we came last month and met with the forum chair, was a big achievement," Panuelo said.

"It was a big surprise for us that Kiribati is not on board."

The Suva Agreement, Panuelo said, had succeeded in achieving reforms the Micronesian subregion had asked for, and in 18 months Micronesia would take on the secretary-general position for five years.

"I think that's a very reasonable achievement, to also have a subregional office in Micronesia of the Pacific Islands Forum and also the Pacific Ocean Commissioner's office to be in Micronesia," he said.

FMS, the Marshall Islands, Nauru and Palau had agreed to the terms in the Suva Agreement.

Three nations had already signed up to it in June, and Nauru was expected to endorse it this week during the PIF Leaders Meeting.

"Our preference is to humbly invite Kiribati to come on board," Panuelo said. "When one is not on board with the Pacific family we're not quite there yet."

The four MPS leaders as well as Fijian prime minister and forum chair Frank Bainimarama had been trying to reach out to the Kiribati government, but had not had any success.

There had been concerns China had been exerting its political influence behind the scenes, prompting Kiribati to isolate itself from the forum.

But the Chinese foreign ministry denied allegations Beijing had any part in Kiribati's stance, calling it "groundless."

"For years, China and the PIF have sound cooperative relations. I would like to stress that China does not interfere in the internal affairs of Pacific Islands countries (PICs) and hopes to see greater solidarity and closer cooperation among PICs for common development," spokesman Wang Wenbin said.

Pacific lead at the Griffith Asia Institute's Pacific Hub, Dr Tess Newton Cain said Kiribati had been on an "isolationist" path for some time.

"We've had not allowing in international media - the media in Kiribati is active but doesn't get a lot of access, doesn't get access to leaders.

"We've had suspensions of High Court justices," Dr Cain said.

"So, there's been this kind of steady move away from the Pacific Islands Forum, or just regionalism, generally, and also, I think there's been a retreat from democracy."