Robert Kabera, a former Rwandan army sergeant major and critic of President Paul Kagame, was found beheaded in Uganda, according to BBC News Africa.
Kabera, aged 50, fled Rwanda citing political persecution after being accused of sexual assault, which he denied.
His body was discovered by local residents outside Kampala over the weekend, but his head remains missing, said Ugandan police spokesperson Kituuma Rusoke.
The Rwandan government has not commented on the killing. Several critics of Kagame have previously been killed within and outside Rwanda.
Jeanne d'Arc Rwigema Uwizeye, Kabera's widow, expressed fear for her family's safety, stating they lack security, according to a statement to BBC Great Lakes.
According to family, Kabera was inspecting a construction site 45 km outside Kampala before his death.
The Rwanda National Congress, an opposition group in exile, called for a comprehensive investigation and justice for those responsible.
The incident raises concerns regarding the safety of Rwandan dissidents living abroad. Kabera's murder echoes the case of Patrick Karegeya, a former intelligence chief found dead in 2014 in Johannesburg.
