Some 50 people, including 3 Americans, appeared in a military court in the Democratic Republic of Congo on Friday in connection with last month's failed coup.
They are facing charges including terrorism, attempted assassination, illegal possession of weapons and arms of war, and financing of terrorism related to the "attempted coup" on 19 May.
Six people were killed during the attack led by little-known opposition figure Christian Malanga, which targeted the presidential palace and a close ally of the President Felix Tshisekedi.
Army officials say Malanga, who lived in the United States, was shot dead for resisting arrest soon after live-streaming the attack.
Malanga's son Marcel, who was born in the US, appeared alongside fellow Americans, Tyler Thompson and Benjamin Reuben Zalman-Polun.
They were lined up on plastic chairs before the judge in the military court in Kinshasa on the first day of the hearing along with the other defendants.
Human Rights Watch has called on the DRC government to accord the accused a fair and transparent trial.
The US embassy said on Monday it had not had access to its citizens to provide consular services. All three have requested an interpreter to translate from French to English.
Many of the charges they face are punishable by death.