Pacific Islands Forum leaders gathered on a remote Cook Islands atoll to discuss issues facing the region Thursday, ahead of US Secretary of State Hillary Clinton's arrival at the summit.

Members of the 15-nation grouping held a retreat on Aitutaki, about a 45-minute flight from the main island Rarotonga, to thrash out a joint communique on issues such as climate change, marine conservation and Fiji.

The communique is scheduled for release later Thursday, hours before Clinton flies in on the first stop of a swing through the Asia Pacific region.

Clinton will arrive in Rarotona late Thursday, becoming the most senior US official to attend the summit in its 43-year history.

Her trip is being seen as a pointed message to China that Washington wants to re-engage in the South Pacific, where Beijing's influence has grown in recent years.

Australian Prime Minister Julia Gillard was forced to cut short her trip to the summit Wednesday to return to Canberra following news five troops had been killed in Afghanistan, the Australian military's deadliest day since Vietnam.

However, Canberra will still be represented at the leaders' retreat and is expected to resist lobbying by some small island states to re-admit Fiji, which was suspended in 2009 in the wake of a military coup three years earlier.

Australia and New Zealand are reluctant to allow Fiji back into the forum until elections scheduled for 2014 have been completed.

The military regime in Suva reneged on a promise to hold elections in 2009 and New Zealand Prime Minister John Key said he would remain cautious about its intentions until the 2014 vote had been held.

"We will obviously point out we really don't think Fiji should be allowed back into the forum in full until they actually have democratic elections and the military are back in the barracks," he told reporters Wednesday.

The communique will also address climate change, a major issue for many of the low-lying island states, which are in danger of being swamped if global warming causes sea levels to rise.

Another issue will be protecting the Pacific's marine environment, one of the last pristine ocean eco-systems, with valuable species such as tuna.

Host nation the Cook Islands announced the creation of the world's largest marine park, a vast swathe of ocean almost twice the size of France, at the summit's opening ceremony on Tuesday.