According to outlet, leaders and members of the Chadema and ACT-Wazalendo were taken for inciting unrest after they vowed to call for protests against the October 28 general elections and demand a repeat of the polls.
Chadema chairman Freeman Mbowe and former mayor of Dar es Salaam Boniface Jacob were among the high profile detainees, the outlet reported.
“We are holding them alongside several other people for inciting people to demonstrations,” the city’s police chief Lazaro Mambosasa was quoted as saying.
The Citizen reported heavy police presence in public areas of the city but no signs of gatherings or protests.
The two parties held a joint press conference on Saturday where they claimed that widespread fraud and rigging took place and called for rejecting the results and organizing new voting.
The US and UK have expressed concern over reports of interference in the election and “heavy-handed policing in the elections”. The UN Office of the High Commissioner for Human Rights, meanwhile, expressed concern over reports of violence against candidates in the run-up to the election.