The United States has sanctioned Tanzania's police chief and barred him from entering the country, over allegations of “torture and sexual assault” of two human rights activists last year.

Washington’s Secretary of State, Marco Rubio, on Thursday said there was “credible information” linking Faustine Jackson Mafwele to gross human rights violations.

Kenyan Boniface Mwangi and Ugandan Agather Atuhaire travelled to Tanzania in May last year in solidarity with detained opposition leader Tundu Lissu, who is facing a treason trial and a potential death sentence.

But the two activists were themselves detained and both claim they were tortured and sexually assaulted.

The alleged they were held "incommunicado" for several days by security forces, before being dumped near their respective borders.