Lusaka - Zambia's opposition leader and defeated presidential candidate Hakainde Hichilema was arrested on Wednesday on charges of sedition and unlawful assembly, police said.
Hichilema, who disputed the result of August polls which re-elected President Edgar Lungu, was detained along with Geoffrey Mwamba, the vice-president of his United Party for National Development (UPND).
"They have been arrested and detained for seditious practices and unlawful assembly," Charity Katanga, police commissioner for Copperbelt province, said, adding that they are to appear in court Thursday.
The alleged unlawful assembly took place on September 26 in the central city of Mpongwe, in the heart of the mineral-rich province.
Sixty-one of their supporters have also been arrested while protesting the party leaders' arrest, and charged with conduct likely to cause a breach of the peace, Katanga said.
Hichilema, a wealthy businessman who has run five times for president, and his deputy are being held in Luanshya, a mining town where they had tried to visit a number of detained supporters.
"After more than three hours of so-called interrogation at Luanshya police station ... we have been arrested and (are) currently in detention for alleged seditious practices and unlawful assembly," Hichilema wrote on his Facebook page.
"We knew it would come to this as a way to silence our voices and weaken our demands for justice to prevail over the stolen elections," he added.
"But that will not stop our resolve for a free Zambia where people's freedoms and liberties have to be reclaimed under a prosperous and united country."
Hichilema has accused Lungu, the country's election commission and court judges of all being guilty of fraud over the August 11 election, which Lungu won by barely 100 000 votes.
Lungu, 59, first took office last year after beating Hichilema in a snap election, and has since faced falling prices for copper - the country's key export - soaring unemployment and inflation rising to over 20%.
Zambia is known for its relative stability but the election campaign was marked by clashes between supporters of Lungu's Patriotic Front (PF) and Hichilema's UPND.
Zambia last held a peaceful transfer of power to an opposition party in 2011 when Michael Sata became president.
Sata died in 2014, and the 2015 election gave Lungu the right to finish Sata's term.
Lungu, a trained military officer and lawyer, has used his short stint in office to present himself as the rightful heir to Sata, who enjoyed widespread popularity.