The call made at the Pacific Island Forum (PIF) conference of leaders came as Bainimarama, Fiji's army chief, declared that he might continue in power for another 10 years.
Australia and New Zealand injects tens of millions of dollars each year into government and non-governmental programmes in Fiji, whose economy has been devastated by decades of political instability.
Bainimarama, whose 2006 coup was Fiji's fourth since 1987, had promised the PIF a year later that he would call elections by April this year.
Poll date appeal
The PIF wants Bainimarama to fix an election date by May 1 with a view to holding democratic elections later this year.
"More than two years of rule by an unelected military government, with no clear timetable for the return of constitutional government to the people, is not acceptable by international standards," the leaders said.
"More than two years of rule by an unelected military government is not acceptable by international standards"
Pacific Island Forum conference of leaders
The PIF statement stopped short of immediately suspending Fiji, an action never taken against a member-state in its more than 30-year history.
Responding to the appeal, Bainimarama rejected the demand, comparing the ultimatum to a declaration of war.
Aiyaz Sayed-Khaiyum, Fiji's attorney-general and representative at the meeting, said the government is legitimate and was determined to complete electoral reform before holding elections.
The country wanted "long-term and sustainable" democracy, a notion which "seems lost on some people", he said.
The US, backing the PIF move, said it "strongly endorses" the call and urged Fiji's interim government to move quickly to restore democracy through free and fair elections.
Robert Wood, a spokesman for the US state department , said in a statement that the US was disappointed that Bainimarama was not at the meeting in Port Moresby.