Democratic Alliance (DA) leader Mmusi Maimane has described Zambian opposition leader Hakainde Hichilema's treason trial as "a political witch hunt by an increasingly threatened President [Edgar] Lungu".
A magistrate ruled on Thursday that Hichilema was to go on trial for treason charges at the High court.
Hichilema and his party tweeted the news.
In a statement, Maimane slammed the decision: "The Democratic Alliance condemns this decision, which is nothing but a political witch hunt by an increasingly threatened President [Edgar] Lungu. Mr Hichilema’s arrest and detention on trumped-up charges in April is an attack on democracy and threatens to destabilise Zambia," said Maimane.
Hichilema was arrested in April for allegedly failing to give way to President Lungu's motorcade and has so far been held in detention for nearly two months.
The incident led to the leader of the United Party for National Development being accused of endangering Lungu's life and treason charges followed.
Maimane said the DA stood in solidarity with the Hichilema.
"The DA stands in solidarity with Mr Hichilema and we will continue to focus global attention on this shameful treatment at the hands of an increasingly autocratic government.
"The DA is committed to seeing improved protections of human rights for all. Until every person has the same protections in terms of the law we will not be free as people on the African continent," said Maimane.
He said he was ready to travel to Zambia once a dated for Hichilema's trial was set.
"Once a date has been set for the trial, I aim to travel to Zambia to attend his trial and give him my full support," he said.
Maimane tried to visit Hichilema in Zambia last month but was barred from entering the country.
The treason case came after Hichilema made a fifth unsuccessful bid for the presidency last year.
He refused to recognise Lungu as president and has challenged the narrow poll defeat in court.