More than 24 hours after the polls closed in presidential, parliamentary and local elections, only a trickle of results had emerged.
Tendai Biti, secretary general of the main MDC opposition party, told diplomats and observers that early results showed it was victorious. "We have won this election," he said.
Projections from 12 percent of the vote showed MDC leader Tsvangirai winning 67 percent nationally, Biti said.
Results usually begin emerging soon after polls close.
Officials said the delay was caused by the complexity of counting in three different polls but Biti expressed concern.
"We're aware the results are final in most constituencies but they are deliberately taking their time to announce (them)...The whole idea of having an election is so you can have a result," he said.
"COUP D'ETAT"
Zimbabwe's security forces, which have thrown their backing firmly behind Mugabe, said before the election they would not allow a victory declaration before counting was complete.
Government spokesman George Charamba warned the opposition against such claims. "It is called a coup d'etat and we all know how coups are handled," he told the state-owned Sunday Mail.
Residents in the eastern opposition stronghold of Manicaland said riot police stopped a victory demonstration by about 200 MDC supporters on Sunday. There was no violence, they said.
The United States said it was worried by the conduct of the election and the absence of most international observers.
"The Mugabe regime is a disgrace to the people of Zimbabwe and a disgrace to southern Africa and to the continent of Africa as a whole," Secretary of State Condoleezza Rice told reporters during a visit to Jerusalem.
Zimbabwe is suffering from the world's highest inflation rate of more than 100,000 percent, chronic shortages of food and fuel, and an HIV/AIDS epidemic that has contributed to a steep decline in life expectancy.
Mugabe accuses the West of sabotaging Zimbabwe's economy. He rejected vote-rigging allegations.
