The pair, Angela Quintal - CPJ's Africa program coordinator, and Muthoki Mumo - its sub-Saharan Africa representative were detained in their hotel rooms in Dar es Salaam, Quintal said.
Quintal and Mumo were then escorted from the hotel and have been taken to an unknown location.
"We continue to engage with our Government of Tanzania counterparts on a wide range of issues, including those related to human rights", read a statement from the State Department adding that it remains committed to values od democracy, rule of law and freedom of expression among others.
South African journalist, Angela Quintal and her colleague Muthoki Mumo have been freed from detention in Tanzania.
Dirco confirm safety of journalists in TanzaniaAngela Quintal: What happened?
The duo was returned to their Dar es Salaam hotel early on Thursday morning after being detained by Tanzanian authorities for five hours on Thursday night for undisclosed reasons.More news: Nintendo will cut offensive imagery from 'Super Smash Bros. Ultimate'
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On Thursday morning, the South African high commissioner will meet with the Tanzanian authorities to assess the situation.
"The tweet by @angelaquintal was not sent by her", wrote Quintal's niece Genevieve Quintal, also a journalist.
In a post on her Facebook page, Quintal said: "SOS we are being taken away for interrogation in Dar".
"We believe that the detention of journalists is a direct and risky threat to media freedom and access to information".
Reporters Without Borders, a pressure group, ranked Tanzania 93rd out of 180 countries worldwide in its 2018 World Press Freedom Index, down 10 places from the previous year.
While they are no longer in custody, Mabaya said Tanzanian authorities have their passports. "One paper chose to suspend publication itself after publishing a story it feared might irritate officials.There have also been more violent incidences of harassment".