A Kigali court on Thursday denied bail to Paul Rusesabagina, whose actions during the 1994 Rwandan genocide inspired the Oscar-nominated film "Hotel Rwanda", ahead of his trial on numerous charges including terrorism.
Rusesabagina, who has become a high-profile government critic and has been living in exile for years, appeared last month under arrest in Kigali in murky circumstances, with his family alleging he was kidnapped abroad.
Prosecutors on Monday slapped him with 13 charges including terrorism, financing and founding militant groups, murder, arson and conspiracy to involve children in armed groups.
"The court finds that the charges by the prosecution against Rusesabagina are grave and serious," Judge Dorothy Yankurije said as she blocked his bail request.
"The court ordered that Rusesabagina be detained provisionally for at least 30 days pending his trial."
Rusesabagina instantly announced he would appeal the decision. He has five days to do so.
He had asked to be released to seek medical care.
The 66-year-old is a cancer survivor and suffers from a heart condition and hypertension, both requiring ongoing medication, his family have said previously.
"The health concerns brought by Mr Rusesabagina are baseless since he does not show how being in detention prevents him from accessing all the medical attention he needs," the judge said.
Rusesabagina, who was played by Don Cheadle in the 2004 film in an Oscar-nominated role, has lived abroad since 1996 and holds both Belgian citizenship and a US Green Card.
Two observers from the US embassy attended the brief hearing.
Rusesabagina became famous as the former manager of a luxury hotel who sheltered hundreds of Tutsi during the genocide in which some 800 000 mostly Tutsi but also moderate Tutsi were killed.
After the genocide, Rusesabagina - a Hutu - became increasingly critical of President Paul Kagame's Tutsi-dominated government, accusing his ruling party of authoritarianism and anti-Hutu sentiment.
At home, as Rusesabagina's fallout with the government grew, so did questions over his heroic tale, with survivors accusing him of profiting off their misery.
He co-founded an opposition group the Rwandan Movement for Democratic Change (MRCD), which is said to have an armed wing called the National Liberation Front (FLN).
In multiple speeches, Rusesabagina has expressed support for the FLN - which has carried out armed attacks and is described as a terrorist organisation by Rwanda - but the extent of his involvement in its actions is unclear.
In his address to the court on Monday, Rusesabagina denied forming the FLN, saying their actions should be blamed on them alone.
He admitted sending some 20 000 euros ($23 000) to FLN commander Callixte Nsabimana - who is on trial on similar charges - but said this was personal assistance to a friend and not for rebel activities.