Nigerian opposition and activists are calling for the release of Daniel Ojukwu, a journalist working with the Foundation for Investigative Journalism (FIJ).
Mr Ojukwu was arrested last Wednesday in Lagos after police accused him of violating the country’s cyber-crime laws, local media reported.
He was reportedly transferred to the Nigeria Police Force National Cybercrime Centre, NPF-NCCC, on Sunday.
Mr Ojukwu's arrest is linked to an investigative story he reported last November involving a senior government official, the FIJ said.
Police spokesperson Muyiwa Adejobi said the journalist had a case to answer after a petition was filed against him. It is not clear who the petitioner is.
His prolonged detention has triggered public outrage on social media as family and media lobby groups demand his unconditional release.
"It is not only irresponsible to arrest journalists for exposing the ills that abound in this government, it is also a breach of their constitutionally guaranteed free press," former Vice-President Atiku Abubakar posted on X platform.
Amnesty International has also condemned the journalist's detention, describing it as "draconian".
Nigeria is ranked 112th out of 180 countries in the World Press Freedom Index by the latest Reporters Without Borders (RSF) report.
It remains one of West Africa’s most dangerous and difficult countries for journalists, according to RSF.
The February and March 2023 general elections saw attacks on nearly 20 journalists and media outlets.