The family of a former Rwandan intelligence chief killed in a Johannesburg hotel has held a memorial service for the ex-spymaster turned critic of Rwandan President Paul Kagame.

Patrick Karegeya's family and colleagues in an opposition coalition accuse Kagame of ordering his assassination. A week ago, the Rwandan leader said it's a matter of time before those who have betrayed Rwanda face consequences.

Karegeya's nephew David Batenga says a memorial service was held Sunday in a Johannesburg chapel, ahead of the burial later in the day.

Police in Mozambique say they have detained four Rwandans, including a senior military official, suspected of involvement in killing Karegeya, who had been living in South Africa since 2007. His body was found on New Year's Day.