Freeman Mbowe was detained with three other opposition figures ahead of calls for mass demonstrations after a controversial election.
The opposition has demanded a repeat vote citing widespread irregularities and called for protests against the outcome, which returned President John Magufuli to the office with 84 percent of the vote.
- Tanzania main opposition parties demand election rerun
- Magufuli wins Tanzania’s presidency for a second term
Those arrested with Freeman Mbowe include a former member of parliament Godbless Lema, the former mayor of Dar es Salaam, Isaya Mwita, and the former mayor of Ubungo municipality, Boniface Jacob.
“I got a message around midnight that they had been taken in,” Lissu said on Monday.
Mwananchi, a privately owned daily that publishes in Swahili, quoted Dar es Salaam’s regional police commander Lazaro Mambosasa as saying they detained Mbowe and other opposition leaders.
Lissu previously said he will not accept the eventual election results.
The vote “marked the most significant backsliding in Tanzania’s democratic credentials”, Tanzania Elections Watch, a group of regional experts said in an assessment released on Friday. It noted a heavy deployment of military and police whose conduct created a “climate of fear”.
The United States has said it was concerned about reports showing “systematic interference in the democratic process”, while the United Kingdom said it was “troubled by the reports of violence and heavy-handed policing in the elections”.