Opposition politicians in Zambia have condemned the arrest of a prominent musician and anti-corruption campaigner.

Police say Chama Fumba, who performs under the name Pilato, was arrested on Saturday for addressing an unauthorised rally in the southern city of Livingstone.

Two human rights activists who travelled from the capital, Lusaka, to Livingstone to secure his release on police bond were detained on arrival. All three are still in police custody.

If convicted of unlawful assembly, Pilato faces up to five years in jail.

He was arrested in 2015 for a song that was deemed to be critical of President Edgar Lungu.