A retired Rwandan army major and 24 others have appeared in a military court in the capital, Kigali, on charges of conspiring against the government.
Habib Mudasiru, 54, and his co-accused have not yet been asked to plead.
The group is made up mostly of Rwandans, but includes Burundians and Ugandans.
They were reportedly captured in June during clashes between the Democratic Republic of Congo’s army and rebel groups in DR Congo’s South Kivu province.
The group is accused of being part of the Rwanda National Congress, led by Gen Kayumba Nyamwasa (pictured), a former army chief who fell out with President Paul Kagame.
In court, no details were given on how the suspects got to Rwanda.
Rwanda’s government repeatedly denies having soldiers in DR Congo to fight rebel groups opposed to it.
Last month, Sylvestre Mudacumura, the leader of the Democratic Forces for the Liberation of Rwanda (FDLR) militia group, was shot dead by DR Congo’s army in North Kivu province.
The FDLR alleged that Rwandan troops were part of operation that led to their leader being killed.
Rwanda denied the allegation.