Mr Savimbi's strident broadcast on his Unita movement's Voice of the Black Cockerel radio station came as the National Electoral Council announced that, with nearly half of the votes counted, President Jose Eduardo dos Santos was leading the presidential election by a 58 to 32 margin.
His charges of vote-rigging and intimidation by the ruling Popular Movement for the Liberation of Angola (MPLA) contradicted the intital judgements by a host of international observers that the elections were free and fair.
'The MPLA wants to cling to power illegally, tooth and nail,' Mr Savimbi said. Failure of the dos Santos government to halt the alleged vote-rigging, he added, 'will all lead Unita to take a position which might deeply disturb the situation in this country'.
Mr Savimbi's speech appeared to be an attempt to bolster morale among Unita militants as the prospect emerged of defeat at the polls. The former guerrilla leader was especially irked by unofficial returns from the state-controlled broadcast media, predicting his impending defeat, and he urged supporters not to watch television or listen to the radio.
Mr dos Santos's lead was expected to narrow as late returns from the rural areas in the central highlands - where Unita enjoys great support - reached the vote counting centre in Luanda. If neither candidate wins more than 50 per cent of the vote, there will be a run-off ballot. Last week's elections, the first since Angola gained independence from Portugal in 1975, were the culmination of the agreement of May 1991, brokered by the United States, the Soviet Union and Portugal. It ended 16 years of civil war that cost at least several hundred thousand lives and laid waste to a fertile country which, endowed with oil and diamonds, is potentially one of richest nations in Africa.
The civil war erupted in 1975 when the transitional government, set up to oversee elections, collapsed amid street fighting in Luanda among the MPLA, Unita and Holden Roberto's National Front for the Liberation of Angola (FNLA).
While calling on his supporters to remain calm yesterday, Mr Savimbi suggested that Unita was prepared to renew the armed struggle. 'There are men and women in this country who are ready to give their lives so that the country can redeem itself,' he said.
Few military observers doubt Mr Savimbi's capacity to cause trouble. The two warring armies officially merged last week into one 'Angolan Armed Forces', under the joint command of General Antonio dos Santos Franca, of the former government army, and the Unita commander, General Arlindo Isaac Chenda Pena. But the new army, trained by British, French and Portuguese instructors, is still in its infancy, with only 8,800 of its planned 50,000 troops having assumed duties.
It is believed that Mr Savimbi still commands the loyalty of his highly disciplined rebel army, and United Nations officials have expressed concern that food meant for demobilised troops and their families has been stockpiled. The former government army, on the other hand, has been plagued by repeated mutinies by soldiers demanding to be demobilised and sent home.
However, there is little chance that Unita's foreign supporters - South Africa and the United States - will back armed action. Western diplomats said yesterday that they were urging Mr Savimbi to stay calm and to make public any complaints about the election.
Mr Savimbi yesterday praised the UN for assisting with the ceasefire and the elections, but warned that he might not accept the international community's judgement on the fairness of the vote. 'Angolan interests come ahead of any accommodation with international opinion, which is foreign opinion,' he said.