Tanzania's main opposition party has threatened to launch mass protests after accusing the authorities of the "killings and abductions" of its members.
The Chadema party said late Wednesday that it would take to the streets of the commercial capital Dar es Salaam on September 23 unless recent disappearances were investigated and missing members "brought back alive or dead".
There had been hopes that Tanzania was entering a period of democratic freedom under President Samia Suluhu Hassan, who took over from her authoritarian predecessor John Magufuli when he died suddenly in March 2021.
She has eased restrictions on the opposition and media, but rights groups are concerned by recent crackdowns, including a mass detention of Chadema members at a rally last month.
At the weekend, Ali Mohamed Kibao, a member of Chadema's national secretariat and a former intelligence officer, was found dead after being abducted, beaten and doused with acid, according to party leader Freeman Mbowe.
"We have resolved to demonstrate in efforts to protect our lives and our country," Mbowe told cheering members at party headquarters on Wednesday.
"This time around, we are not joking," he added.
Mbowe said five Chadema officials had gone missing recently, though one appeared in court after several weeks and was denied bail.
The Tanganyika Law Society said last month that 83 people were either kidnapped or went missing between 2016 and 2024.
Mbowe called for the resignation of Tanzania's home minister, and heads of police and intelligence over the disappearances.
He also called for British police to be called in for an investigation.
"We propose the UK's Scotland Yard to probe killings and abductions of people in the last two years. Tanzanian security agents are the first suspect," Mbowe said.
Hassan had expressed her "great sadness" over the death of Kibao and called for an investigation.
"Our country is democratic, and every citizen has the right to live. The government I lead will not tolerate such acts of cruelty," she said.
