LUSAKA (Reuters) - A Zambian court refused on Wednesday to throw out treason charges against opposition leader Hakainde Hichilema, a case that has stoked political tension months after contested elections.

United Party for National Development (UPND) Presidential candidate Hakainde Hichilema looks on during a rally in Lusaka January 18, 2015. REUTERS/Rogan Ward/File Photo

The United Party for National Development (UPND) leader was arrested in a police raid on his home earlier this month and charged with trying to overthrow the government.

Hichilema’s lawyers appealed, saying the charges were too vague. But Magistrate Greenwell Malumani told a packed hearing his court did not have the authority to quash the charge and referred the case up to the High Court.

Defense lawyers on Wednesday asked that the prosecution call its witnesses so that the new magistrate could hear if there was strong evidence to take to the High Court.

Zambia was seen as one of southern Africa’s most stable countries until relations soured between the government and opposition in August, when President Edgar Lungu’s Patriotic Front (PF) party beat the UPND in elections marred by violence.

The opposition says the vote was rigged but Hichilema has so far failed in his legal challenge against the result.

Police this month initially accused Hichilema of treason on the grounds that he had refused to give way to Lungu’s motorcade as it passed through Mongu, a town west of the capital Lusaka.

Hichilema and his co-accused were later charged with plotting with other people between Oct. 10 last year and April 8 this year to overthrow the government by unlawful means.

The treason charge read in court by magistrate David Simusamba asserts that the accused on April 5 conspired to ensure that Hichilema was declared President of Zambia.

The six were also charged with obstructing Lungu’s motorcade on April 8, described as an action that could have killed the President or caused harm to him in order to usurp power.

“It all amounts to a witch-hunt. We are shocked that the state keeps changing the details of the treason charge,” UPND spokesman Charles Kakoma told Reuters.