A Kenyan and a Ugandan human rights activist who were detained in Tanzania for several days last month said on Monday that Tanzanian security officers sexually assaulted them while in custody.

Spokespeople for Tanzania's government, foreign affairs ministry and police did not immediately respond to requests for comment on the allegations by Kenya's Boniface Mwangi and Uganda's Agather Atuhaire.

The spokesperson for Kenya's Ministry of Foreign Affairs and Uganda's information minister did not respond to calls seeking comment.

Mwangi and Atuhaire were detained after arriving in Dar es Salaam to attend the first court appearance of Tanzanian opposition leader Tundu Lissu, who faces treason charges.

Tanzanian authorities have not commented on Mwangi and Atuhaire's detentions, though in public remarks on May 19, the day they were detained, President Samia Suluhu Hassan warned foreign activists against "invading and interfering in our affairs."

After being taken into custody at their hotel in Dar es Salaam, Mwangi said they were blindfolded by police officers and taken to a house. He said that while questioning him about the whereabouts of his phone and laptop, his interrogators stripped him, blindfolded him and sexually assaulted him.

He cried as he described his ordeal at a press conference in Kenya's capital Nairobi, adding that the security personnel had also photographed him while assaulting him.

Atuhaire said she too had been blindfolded, tied up and similarly assaulted.

Both activists were eventually dumped near the borders of their countries, where they crossed back home.

Lissu, who came second in Tanzania's last presidential poll, was arrested in April and charged with treason over what prosecutors said was a speech calling on the public to rebel and disrupt elections due in October.

The case has highlighted a growing crackdown on opponents of Hassan, whose party has nominated her to stand in the October vote.

She won plaudits after coming to power in 2021 for easing the political repression that had proliferated under her predecessor, but has faced mounting criticism over a series of arrests and unexplained abductions of political opponents.

Hassan has said the government is committed to respecting human rights, and ordered an investigation into reported abductions last year.