Zimbabwe's main opposition party said soldiers were searching the capital for its supporters on Saturday, as others arrested earlier appeared in court.
Nkululeko Sibanda, a top official in the Movement for Democratic Change, spoke at a courthouse in Harare where 24 detained supporters awaited a hearing. Mr Sibanda said they were accused of inciting public violence.
"A lot of people are hiding," he said. "It's scarier than the Mugabe times."
The allegation came a day after election authorities declared incumbent Emmerson Mnangagwa the winner of the July 30 presidential election, a result the MDC dismissed as "fake".
Mr Mnangagwa has said he wants to work with the opposition to rebuild the country after decades of repression under his former mentor, Robert Mugabe.
Mr Sibanda said he was concerned that the government could try to implicate opposition supporters in the deaths of six people who were killed during a military crackdown in Harare on Wednesday. Soldiers opened fire on protesters, some of whom were rioting.
Police raided the MDC headquarters the next day, arresting 18 people. Mr Sibanda said those arrested were at Saturday's hearing. "We know that the government is trying to build a case to say that our party is violent," he said.
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As riot police circulated in the capital, supporters of opposition leader Nelson Chamisa urged him to keep fighting after he forcefully rejected Mr Mnangagwa's election victory and alleged manipulation.
Zimbabwe's electoral commission said the president won with 50.8 per cent of the vote while Mr Chamisa received 44.3 per cent.
Mr Chamisa said the opposition's own count showed he won the vote and that they would challenge the election results in court. "We're doing all to secure your vote & defend your WILL," he tweeted on Saturday.
"What we want Mr Nelson Chamisa to do for us is to not give up on our vote," said one supporter in the capital, Tisi Habis. "No matter what the [Zimbabwe Electoral Commission] says, Mr. Chamisa is our president."
International election observers who were invited by Mr Mnangagwa's government after years of being banned by Mr Mugabe issued mixed reports on the election.
While the election itself was called peaceful, the observers expressed concern over the lack of transparency in the voters' roll and the "extreme bias" of state-run media in favour of Mr Mnangagwa. And in a joint statement the observers criticised the military's "excessive" use of force.
A credible election is a crucial step for lifting international sanctions and attracting badly needed foreign investment in Zimbabwe's long-collapsed economy.
Mr Mnangagwa on Friday claimed the vote had been free and fair, praising the "unprecedented flowering of freedom and democracy in our beloved homeland" while saying he wanted an independent investigation into the deadly unrest.
The US State Department late on Friday encouraged the release of fully transparent election results and said anyone with grievances should pursue them through legal channels. "We encourage all political leaders to show magnanimity in victory and graciousness in defeat," it said.