Zimbabwe's main opposition leader, Nelson Chamisa, has filed a legal challenge against President Emmerson Mnangagwa's recent election victory.
Mr Chamisa says he has evidence to show that he was cheated out of the 30 July presidential election.
His MDC Alliance party say the vote was marred by "mammoth theft and fraud", but the electoral commission has said there was "no skulduggery".
Mr Mnangagwa won 50.8% of the vote compared with Mr Chamisa's 44.3%.
The Constitutional Court will have 14 days to make a ruling on the legal challenge.
The MDC must prove that any irregularities were grave enough to change the outcome of the vote. If it does this successfully the court could order a recount or nullify the result altogether.
Mr Chamisa wants the court to declare him the winner or call a fresh election, his lawyer told Reuters news agency on Friday.
"We have a good case and cause!" he tweeted shortly after filing the challenge.
At least six people were killed two days after the vote in clashes between security forces and MDC Alliance supporters who alleged that Mr Chamisa had been robbed of victory.
There was great optimism that the elections would bring real change after the end of Robert Mugabe's 37-year rule in November.
But the MDC Alliance say the security forces have launched a brutal crackdown on the opposition following the disputed poll.
President Emmerson Mnangagwa narrowly won the recent election
Mr Mnangagwa has appealed for peace and promised an independent investigation into the post-election violence.
By narrowly winning more than 50% of the vote Mr Mnangagwa avoided a run-off election against Mr Chamisa.
But the legal challenge to his victory is likely to delay his inauguration that was scheduled to take place on Sunday.
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