With results trickling in Friday, opposition leader Morgan Tsvangirai accused the government of trying to steal a parliamentary election and urged Zimbabweans to defend their votes.
Tsvangirai's Movement for Democratic change won 31 of the first 54 seats declared Friday, but, citing inconsistencies in the results, said it expected to lose seats overall in the 150-member parliament.
"The government has fraudulently, once again, betrayed the people," Tsvangirai told reporters. "We believe the people of Zimbabwe must defend their vote and their right to free and fair elections."
Tsvangirai said his party would do more this time than merely appeal the result in Zimbabwe's courts - which the government has packed with sympathetic judges. But he would not specify what action it would take.
Previous attempts at protest have been violently crushed by security forces and members of the ruling party's youth militia, and the MDC has shied away from confrontation in recent years.
Independent Zimbabwean rights groups and the United States, whose diplomats in the country observed the campaign and voting, agreed with Tsvangirai that the polls were seriously flawed. They said that though this campaign had been relatively peaceful, bloodletting and intimidation in previous years had already skewed the poll in favor of President Robert Mugabe's party.
But observers from neighboring countries largely sympathetic to Mugabe said Thursday's poll was conducted in an "open, transparent and professional manner."
A delegation from the 14-member Southern African Development Community - which also endorsed a 2002 presidential poll Western observers said was marred by widespread violence, intimidation and vote rigging - said they were convinced the count also would be legitimate. But it said in a statement it was concerned about the high number of people who were unable to cast ballots.
The MDC won 57 of Parliament's 120 elected seats in the last legislative poll in 2000, but lost six seats in subsequent by-elections. Mugabe appoints an additional 30 seats, virtually guaranteeing his Zimbabwe African National Union-Patriotic Front a majority.
In 2002, Tsvangirai was narrowly declared loser of the presidential poll.
The seats won so far by the opposition MDC on Thursday were largely in its urban strongholds. A ruling party official, William Nhara, predicted Friday that the party would win almost all the remaining seats.
Mugabe's nephew, ruling party candidate Patrick Zhawao, was declared the winner in Manyame, 40 kilometers (25 miles) southwest of Harare, in a what the MDC charged was the first example of vote manipulation by the government.
Election officials announced Thursday night that 14,812 people voted in that constituency. But early Friday, they changed the total to 24,000 and said Zhawao got more than 15,000 votes. MDC officials pointed to that as a sign of more trouble to come. Election commission officials refused to comment on the discrepancy, but said they doubted there was any rigging.
Under international pressure to produce a credible result, Mugabe's government and party ratcheted down the violence in the last weeks of campaigning before Thursday's vote.
But the independent Zimbabwe Election Support Network, which deployed 6,000 observers nationwide, said as many as a quarter of those who tried to vote before 3:15 p.m. (1315 GMT) Thursday were turned away because their names did not appear on the voter roll, or they failed to present proper identification.
George Chiweshe, a former army officer who heads the Zimbabwe Electoral Commission, conceded some were turned away but said the problem was not as big as the independent group estimated. He said 116,198 of the 1.4 million people who tried to vote before 2 p.m. (1200 GMT) - less than 10 percent - were not allowed.
The country was plunged into political and economic chaos when Mugabe's government began seizing thousands of white-owned commercial farms for redistribution to black Zimbabweans after the last legislative poll in 2000. Combined with years of drought, the often violent program has crippled agriculture - the country's economic base.
The past five years have also seen a crackdown on dissent. Restrictive security and media laws were passed, opposition leaders jailed, and a number of independent newspapers shut down.
RODRIQUE NGOWI Associated Press Writer
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