Fiji is facing an international backlash after military commander Frank Bainimarama last night sacked the Government of Laisenia Qarase and imposed virtual martial law.
Commodore Bainimarama claimed his actions were legal under the doctrine of necessity, which covers exceptional circumstances such as when a government is unable to operate.
But at the United Nations, Secretary-General Kofi Annan condemned the takeover and called for the restoration of the elected government, while chief UN spokesman Stephane Dujarric said the upheaval could affect Fiji's future participation in UN peacekeeping operations.
Washington said it had temporarily suspended about US$2.5 million ($3.67 million) in US aid to the South Pacific island nation.
US State Department spokesman Sean McCormack said: "We condemn the action that Gen Bainimarama has taken. We call for those forces who are attempting to seize control of the Fijian government to stand down."
Britain has cut its military ties with Fiji, with Foreign Secretary Margaret Beckett describing the coup as "wholly unconstitutional".
'We are suspending immediately bilateral and military assistance to Fiji and considering further measures with our international and Commonwealth partners," Prime Minister Tony Blair's official spokesman said.
Commonwealth Secretary General Don McKinnon said Fiji was likely to be suspended from the Commonwealth.
"The likelihood of Fiji being suspended is very high," he told reporters, adding that the Commonwealth "unreservedly condemns any military action against a democratically elected government".
Foreign ministers from nine Commonwealth countries will meet in London on Friday to discuss the situation.
The EU expressed its "strongest possible opposition to actions that undermine the democratic process in Fiji" and urged the military to hand back power to Qarase's government.
New Zealand Prime Minister Helen Clark said Commodore Bainimarama had ripped up his country's constitution.
New Zealand has cut ties with Fiji, banning senior military officers from visiting New Zealand and suspending military links. Helen Clark said Fijian sports teams would not be able to play in New Zealand and aid to Fiji had been frozen and would be reviewed.
Australia has also imposed sanctions and sent three warships in case it needed to evacuate holidaying nationals.
The coup is expected to severely damage Fiji's fragile sugar and tourism industries, as it did in previous upheavals.