"I hereby confirm I have abrogated the 1997 constitution and appointed myself as head of state in the new order," he said.
"I will soon be inviting suitable individuals to join or rejoin the bench under the new order."
Fiji remained calm following the announcement but police have stepped up security across South Pacific nation.
Journalist sources in Fiji have told Al Jazeera the president has banned local media from discussing or reporting on the new directives.
|Bainimarama has resisted international pressure for democratic elections
The president's move comes a day after Fiji's second-highest court ruled on a challenge to the government of Commodore Frank Bainimarama, the armed forces chief, brought by Laisenia Qarase, the prime minister ousted in a 2006 coup.
Declaring Bainimarama's post-coup military government illegal, the court ordered that Iloilo appoint a distinguished person to act as caretaker prime minister, but said that person should neither be Bainimarama nor Qarase.
Following the ruling Ban Ki-moon, the UN secretary-general, appealed for calm and urged "full respect for human rights, the rule of law and the judicial process".
In his address Iloilo said he would appoint a new interim government until elections can be held in 2014, saying that "the machinery of government must continue".
Bainimarama was appointed caretaker prime minister three years ago following a military coup, the fourth in the South Pacific nation in two decades.
Responding to Thursday's court ruling Bainimarama said on national television he had resigned from the prime minister's post, and said that the security forces would continue to maintain law and order.
The armed force's chief who led the 2006 coup had resisted international pressure, led by Australia and New Zealand, to restore democracy and hold elections this year under the existing constitution.
Analysts have said Iloilo may yet reappoint Bainimarama to the post of prime minister, and said his address on Friday bore the hallmarks of the armed force's chief.
"It looks like a prepared statement by Bainimarama, delivered by Iloilo," Rod Alley, a senior fellow at New Zealand's Centre for Strategic Studies, told The Associated Press.
"This is extraordinary and doesn't look good for Fiji."
The 16-nation Pacific Islands Forum has threatened to suspend Fiji's membership unless it names an election date by the beginning of next month.
The Commonwealth has threatened similar action by no later than September if sufficient progress is not made towards restoring democracy.
The international isolation has hit Fiji's economy tourism and sugar-export dependent economy hard, threatening to plunge many of its 800,000 population into poverty.