Zimbabwe lawmaker Job Sikhala, vice-chairman of the opposition MDC party, was arrested and charged with treason on Tuesday for allegedly saying he wanted to oust the president.
Sikhala was "formally charged with attempting to overthrow the government unconstitutionally," his lawyer Obey Shava told AFP, saying his client denied the charges.
Some Zimbabweans hoped the fall of long-time autocrat Robert Mugabe in 2017 would usher in a more tolerant climate as President Emmerson Mnangagwa sought to attract foreign investment.
But government critics have been frequently targeted by the police and security forces as the country's economy tips into crisis.
Sikhala, an outspoken senior official in the Movement for Democratic Change party, allegedly said in a speech at a rally on Saturday that the party would unseat Mnangagwa before the next election.
"We are going to overthrow him (Mnangagwa) before 2023 -- that is not a joke," Sikhala was quoted as saying.
He faces a maximum 20 years in prison if convicted of treason.
The ZANU-PF government reacted furiously to Sikhala's remarks, with spokesman Nick Mangwana describing the speech as an "insurgent rant".
The Zimbabwe Lawyers for Human Rights (ZLHR) group said that Sikhala was 21st person to be arrested and charged with treason since January.
Seven rights campaigners were arrested at Harare airport last month and charged with subversion on their arrival from the Maldives, where police allege they attended a workshop on how to topple the government.
Economy in troubles
After protests in January triggered by a doubling of fuel prices, Mnangagwa warned that the authorities would target rights groups deemed to be anti-government.
The authorities blamed the protests on the MDC party and non-governmental organisations that they said were backed by Western nations.
Zimbabwe's police and army have often used brutal force, including live ammunition, to crush dissent.
Mnangagwa had promised a fresh start for Zimbabwe after decades of repression, international isolation and economic decline under Mugabe.
The MDC said Sikhala's remarks had been misconstrued and that the party pursued only peaceful and democratic means to solve Zimbabwe's "national crisis".
Official inflation is at nearly 100 percent -- the highest since hyperinflation forced the government to abandon the Zimbabwe dollar in 2009 -- while supplies of essentials such as bread, medicine and petrol regularly run short.
Power cuts often last 19 hours a day, and the government has banned the use of the trusted US dollar and other foreign currencies that functioned as legal tender for the last 10 years.