Zimbabwe's Movement for Democratic Change opposition party has confirmed it will launch a legal challenge to President Emmerson Mnangagwa's narrow election victory, which it says was due to fraud.
"Those results represent a total negation of the will of the people," MDC lawyer Thabani Mpofu told reporters.
"The election results made by ZEC (Zimbabwe Electoral Commission) will be challenged."
Mr Mpofu declined to give the date when the legal case will be lodged, which is set to delay Mr Mnangagwa's inauguration.
Under Zimbabwean law, the deadline for filing the challenge is Friday.
The Constitutional Court must rule on the petition within 14 days.
"Evidence derives from ZEC's figures that in our view grossly mathematically fail to tally," said Mr Mpofu.
"We have what we require for the purposes not just of mounting a credible and sustainable challenge, but that will yield a vacation of the entire process announced by ZEC.
"We are convinced once this has been placed before a court, there will only be one outcome."
The MDC headquarters were raided by authorities in what Mr Mpofu described as "an attempt to destroy our evidence", but he said their data was "secure".
He gave no details about the evidence of alleged fraud, promising to reveal "a secret weapon" in court.
Mr Mnangagwa, a former ally of ousted president Robert Mugabe, narrowly retained power in last week's landmark vote, but the MDC has repeatedly said it won.
President Mnangagwa, the ruling ZANU-PF party and the electoral commission have dismissed charges of cheating.
Zimbabwe police arrest senior opposition leader
Former Zimbabwean finance minister and opposition politician Tendai Biti has been detained by police as he tried to cross the border and seek asylum in neighbouring Zambia, his lawyer has said.
It comes a day after the authorities said they were looking for Mr Biti in connection with violence following last week's disputed election.
Six people were killed in the army clampdown on protests against the result and Mr Mnangagwa's main rival, opposition leader Nelson Chamisa, has accused the government of a security crackdown on his party's members.
Mr Biti, whose People's Democratic Party had formed an election alliance with Mr Chamisa's MDC, had been in hiding since last week and had feared for his life, his lawyer Nqobizitha Mlilo said.
"We have kick-started processes of seeking political asylum so we are waiting to see how far the processes will go. His life has been in danger," he said.
Police have not yet informed him of the charges, Mr Mlilo added.
A police spokesperson said they had no information on the arrest.
Yesterday the Criminal Investigations Department said that police were looking for Mr Biti, MDC chairman Morgen Komichi and MDC youth leader Happymore Chidziva in connection with last week's violence.
Mr Mlilo said Mr Biti was arrested after presenting himself to Zambian immigration officials at Chirundu border post, 350km north of the Zimbabwean capital Harare, where Zimbabwean and Zambian officials share the same building.
"It seems the Zambian immigration officials alerted the Zimbabwean police and they effected an arrest," said Mr Mlilo who was at the border with Mr Biti.