Tanzania's Faustine Jackson Mafwele is accused of involvement in "gross violations of human rights".
The United States has sanctioned a senior Tanzanian police officer over the alleged torture of two well-known activists a year ago.
Prominent campaigners Boniface Mwangi of Kenya and Agather Atuhaire of Uganda travelled to Tanzania in May 2025 in solidarity with detained opposition leader Tundu Lissu, who is facing a treason trial and a potential death sentence.
But Mwangi and Atuhaire were themselves detained and say they were tortured and sexually assaulted while held "incommunicado" for several days by security forces, before being dumped near their respective borders.
Announcing the sanctions late on Thursday, the office of US Secretary of State Marco Rubio said there was "credible information" that Tanzania's senior assistant commissioner Faustine Jackson Mafwele was involved in "gross violations of human rights".
Banned from US
"One year ago, members of the (Tanzanian Police Force) detained, tortured, and sexually assaulted Ugandan Agather Atuhaire and Kenyan Boniface Mwangi, who were in Dar es Salaam to observe the judicial trial of opposition leader Tundu Lissu," Rubio's office said in a statement.
It said Mafwele was banned from entering the United States.
Atuhaire won an International Women of Courage Award from the US in 2024.
Mwangi is a well-known activist in Kenya who has announced a run for the presidency in next year's election.
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