Fiji was plunged into its fourth coup in 20 years today, after the military ousted the prime minister, Laisenia Qarese, and took control of the government.

The head of the army, Frank Bainimarama, appointed himself temporary president, throwing the South Pacific island state into economic and political disarray and risking international isolation from Australia, the UN and the Commonwealth.

"The military has taken over the government, has executive authority and the running of this country," Mr Bainimarama told a news conference broadcast nationally. He urged all citizens to remain calm.

The long-anticipated coup reached its climax when soldiers turned up at the prime minister's residence and took away his car keys. Armed troops ringed the building, effectively placing him under house arrest.

"The government they want to set up will be totally illegal," Mr Qarase said in an AP television interview. "What the military has done is raped our constitution." He also insisted he would not step down voluntarily.

The Fiji Times newspaper announced on its website that it had suspended publication after the military ordered it not to publish material that might incite trouble.

The paper's editor, Samisoni Kakaivalu, said he refused to edit a newspaper in which content had been altered or censored by external forces. "This is no longer journalism, but propaganda," he said. "I think the military needs to remember an age-old truism: in a battle between guns and pens, pens always win."

Soldiers erected roadblocks around the capital of Suva, and checkpoints were also set up in Nadi, the site of Fiji's international airport and the point of entry for the tens of thousands of tourists who visit every year.

The coup follows tension between the two men over a bill to grant pardons to those involved in the last coup in 2000. Mr Bainimarama also wants to quash legislation he claims favours indigenous Fijians over the ethnic Indian minority.

Nearly 40% of the population are descendants of Indian labourers shipped to Fiji by the British in the 19th century to work in the sugar industry.

During the 2000 coup, in which nationalists stormed parliament and held ministers and MPs hostage for 56 days, Mr Bainamarama achieved hero status for ending the standoff without bloodshed.

Ironically, he was instrumental in the appointment of Mr Qarese, who led the post-coup interim government. But relations between them began to deteriorate when the prime minister released two of the coup plotters after only two months of their two-year prison sentences and subsequently gave them cabinet posts.

Mr Bainamarama is deeply suspicious of Fijian nationalists. Six years ago he narrowly avoided assassination when rebel army officers attempted to kill him while he was at lunch in the officers' mess at Suva barracks.

Since then he is said to have become paranoid about the nationalists, according to Fiji media owner William Parkinson. "He is really concerned that the 2000 events could happen again," he said.

The latest military takeover could damage Fiji's international standing. The Commonwealth will consider suspending the island state later this week, and the UN may curtail the military's peacekeeping role abroad.

The Australian prime minister, John Howard, condemned the coup but turned down a plea from Mr Qarase to send in troops. "I do not think it is in Australia's national interest to become involved in the possibility of Australian and Fijian troops firing on each other," he said.

Although Mr Bainimarama has appointed himself president, he promised to restore executive powers to the former president Ratu Josefa Iloilo by next week. An interim government would then be appointed, with elections to follow at an unspecified date.

The military takeover is not expected to be welcomed by many Fijians, about 80% of whom voted for the government at the last election.

Canberra has urged its citizens to leave Suva, and the Australian navy is standing by to evacuate foreign nationals if necessary.