The leader of Zambia's second-largest opposition group was arrested Tuesday over the killing of a ruling party supporter in the midst of campaigning for a by-election, his party said.
Police detained Hakainde Hichilema, head of the United Party for National Development (UPND), in the tourist town of Livingstone 540 kilometres (336 miles) south of the capital Lusaka, according to party spokesman Cornelius Mweetwa.
"Hakainde has been arrested and is currently under detention with all the people that were with him. His security personnel have also been arrested," Mweetwa told AFP.
Two parliamentarians count among 20 people now arrested over the killing of Harrison Chanda, a member of the ruling Patriotic Front (PF), he added.
"Hakainde was bundled into a police vehicle... As a result people are now rioting, calling for his release," said Mweetwa.
State radio confirmed the arrests, but police were unavailable for comment.
Violence has marred campaigning ahead of parliamentary by-elections Thursday at the site of the world-famous Victoria Falls.
Chanda, a party youth secretary for Monze, another town in southern province, was attacked by a group of people in Livingstone on Monday night and hit on the head with an axe, police said.
The PF-government has lately arrested and charged opposition members for various offences.
Hichilema was also arrested in January and charged with defaming President Michael Sata.