The leaders of Tanzania's main opposition party Chadema have been released on bail, a party spokesman said on Tuesday, after they were detained in a mass roundup ahead of a youth day rally. As many as 520 people were arrested across the country, according to a police statement, before a banned Chadema rally on Monday that had been expected to draw thousands of young people in the southwestern city of Mbeya. But Chadema posted on X on Tuesday that its offices in Mbeya "are surrounded by the police and they are not allowing people to enter the offices".

Rights groups and government opponents have raised fears the police action could signal a return to the oppressive policies of Tanzania's late president John Magufuli. The arrests came despite his successor President Samia Suluhu Hassan vowing a return to "competitive politics" and easing some restrictions on the opposition and the media, including lifting a six-year ban on opposition gatherings. Those released included Chadema chairman Freeman Mbowe and his deputy Tundu Lissu -- both former presidential candidates -- and other top party officials, Chadema spokesman John Mrema said on X.

"(They) have been returned to Dar es Salaam by police and have bailed themselves out", he said but added that "some leaders" continue to be held, without giving further details. Awadh Haji, police chief of operations and training, said "all the top Chadema leaders who were arrested, after interrogation and other procedures, have been returned to.