The two South Africans arrested for "promoting homosexuality" in Tanzania last week were being held in the country's prisons "illegally", the Initiative for Strategic Litigation in Africa (ISLA) said on Monday.
ISLA human rights lawyer Sibongile Ndashe and another South African lawyer were arrested in the Peacock Hotel in Dar es Salaam by Tanzanian police on Tuesday last week.
The name of the second South African has not been released to the media.
Tanzanian law dictates that a suspect should be charged in a criminal court within 24 hours of being arrested, ISLA spokesperson Matilda Lasseko told News24 on Monday.
"The reality is that, if they [the two South Africans] broke any laws, they would've been charged already. What is happening now is illegal - the country is on a witch-hunt against our people," Lasseko said.
Lasseko said the two lawyers were arrested while they were discussing possible litigation against the Tanzanian government for closing down HIV care centres.
Since their arrest last week, the two were granted bail, which was then revoked on Friday when they reported, as required by their bail conditions, to a Tanzanian police station.
"It is quite unfortunate that the Tanzanian government is doing this now, the message they are sending [to citizens] is that if you are planning any legal action against the state, there is ill-treatment coming your way," Lasseko said.
"What the state is saying is that: we will harass you and unlawfully detain you. This goes against the fundamental principle of justice."
Lasseko said she did not know to what extent Tanzanian courts were politically influenced, which might negatively affect the South Africans arrested.
She said, however, that the detained lawyers were in "good spirits" at Dar es Salaam's central police station and were meeting with lawyers who would try and expedite a court appearance.
The South African High Commissioner in Tanzania, Thami Mseleku, said the South African embassy had been in contact with the Tanzanian police since the lawyers' arrest.
Mseleku said he has personally met with the two South Africans, but had been asked by police to "give them space to complete investigations".
The South African embassy was also in continual contact with the Tanzanian department of international relations, as was custom when matters such as these arose, Mseleku said.
The Department of International Relations and Cooperation (Dirco) did not respond to a News24 request for comment and referred all enquiries to the South African embassy.