New Zealand is watching closely as tensions rise between Tonga and Fiji after a former Fijian army chief fled to Tonga after being charged with sedition but does not intend to intervene, Prime Minister John Key says.

Fiji military strongman Commodore Frank Bainimarama has declared ex-Fiji Royal Military Force (RFMF) chief of staff Lieutenant Colonel Ratu Tevita Uluilakeba Mara a fugitive and is seeking his extradition.

Lt Col Mara was picked up by Royal Tongan Navy Patrol Boat Savea a nautical mile northwest of Cape Washington in Kadavu last week.

Lt Col Mara, who has strong Tongan connections, is now reported to be under the kingdom's protection.

"When I was rescued by the Tongan navy, I asked to be brought to Nukualofa, where with the sure protection of King George's government I shall be able to tell the truth without fear of retribution about the tragic oppression that stifles my beloved land," Lt Col Mara said.

He is a son of late Fiji president Ratu Sir Kamisese Mara. Along with Pita Driti, a high ranking commander, Lt Col Mara was charged a week ago with mutiny and accused of trying to overthrow the Bainimarama regime.

Cdre Bainimarama told FijiLive said the extraction was illegal and he would talk toe the Tongan King.

Police had started investigations to find out who facilitated the fleeing of an accused person and conspired to breach Fiji's sovereignty.

"This is unfortunate and shows a fundamental disloyalty to Fiji, Fijian laws and the Fijian people," Cdre Bainimarama said.

Mr Key said today the development was interesting.

"Its a very interesting position and we are obviously monitoring that quite closely, Tevita Mara is the guy who was Bainimarama's right-hand-man when he undertook the coup back in 2006. The fact that he has jumped ship, if you like, is a very interesting development there," he told TV One's Breakfast programme.

Lt Col Mara and his father were important figures in Fiji.

"This is right up there in the leadership of Fiji. We will continue to monitor it, we are not playing any role. It's an issue between, ultimately at this stage, Tonga and Fiji... It's always been quite fragile in Fiji, that's the nature of coups they always are."

New Zealand's position was it would support democratic elections if the leadership decided to hold them.

The diplomatic situation between Tonga and Fiji has recently been tense, with both laying claim to the Minerva Reef which lies between the two countries.