The actions of the three Americans were "punishable by death", judge Freddy Ehume told the military court in the DRC capital, Kinshasa.

Marcel Malanga and Taylor Christian Thomson, both 21, and 36-year-old Benjamin Reuben Zalman-Polun were the first of the defendants to stand before the judge to hear the charges read out against them.

"These acts are punishable by death," the presiding judge of the Kinshasa-Gombe military court told the three.

Another 50 or so defendants then took the stand one by one under a large tent in the grounds of the Ndolo military prison to hear the charges.

All appeared in blue and yellow prison uniforms at their trial, which started at around 11:40 am (1040 GMT) and was followed by western diplomats, journalists and lawyers.

The alleged coup bid occurred on May 19 when armed men attacked the home of Economy Minister Vital Kamerhe in the early hours before moving onto the nearby Palais de la Nation that houses President Felix Tshisekedi's offices.

They were seemingly filmed brandishing the flag of Zaire -- the name of the Central African country during the rule of dictator Mobutu Sese Seko -- and chanting that the government of current President Felix Tshisekedi was over.

The army later announced on national television that security forces had stopped "an attempted coup d'etat".

- Suspected accomplice-

The alleged plot was led by Christian Malanga, a Congolese man who was a "naturalised American" and who was killed by security forces, army spokesman General Sylvain Ekenge has said.

His son, who is a US citizen, was one of the three Americans to face trial on Friday.

Ekenge said around 40 of the assailants, of "various nationalities", had been arrested and a further four killed, including Malanga.

The motive behind the alleged incident remains unclear but the government condemned it as an attempt to "destabilise" the vast country's "institutions".

Four women are among the accused, as well as at least one Belgian national, Jean-Jacques Wondo.

Wondo, a military expert of Congolese origin, was arrested two days after the events, on May 21.

He is accused of being an "accomplice of Christian Malanga" by "providing transport" for the alleged putschists, his lawyer said.

Wondo refuted the charged against him and would defend himself, lawyer Masingo Shela added.

According to a court document, a total of 53 defendants are being tried, including Christian Malanga, even though he is dead.

The charges include "attack, terrorism, illegal possession of weapons and munitions of war, attempted assassination, criminal association, murder (and) financing of terrorism", according to the document.