Zimbabwe's opposition Movement for Democratic Change has filed papers in the country's highest court saying the national election was rigged and calling for a re-run of the vote.
Last weekend the country's Electoral Commission announced President Robert Mugabe was re-elected with just over 61% of the votes, against nearly 34% for Morgan Tsvangirai of the MDC.
Lawyers for the MDC have filed papers with the Constitutional Court in Harare arguing the election should be annulled because of widespread alleged illegalities and intimidation of voters.
The opposition party has alleged hundreds of thousands of voters were turned away, and that the voters' roll was flawed, containing at least 870,000 duplicated names.
ZANU-PF has denied any vote-rigging in the 31 July election, Reuters reports.
African observers broadly approved the presidential and parliamentary elections as orderly and free, but some other countries - including the US and Britain - have questioned the credibility of the poll.
The election outcome extends Mr Mugabe's 33-year rule for five more years. He will be sworn in only after the case is decided.