Marcel Malanga and Taylor Christian Thomson, both 21, and 36-year-old Benjamin Reuben Zalman-Polun are among 50 defendants in the case and were the first to stand before the judge to hear the charges against them.

"These acts are punishable by death," the presiding judge of the Kinshasa-Gombe military court, Freddy Ehume, told the three in the Democratic Republic of Congo's capital.

Defendants wearing blue and yellow prison uniforms took the stand one by one under a large tent in the grounds of the Ndolo military prison to hear the charges.

Around 10 assault rifles and various other pieces of evidence were placed in front of the judges.

Western diplomats, journalists and lawyers were present for the trial, which is set to resume on June 14.

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 Tshisekedi's government 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 a Canadian, a Briton and a Belgian, Jean-Jacques Wondo, who are all naturalised Congolese.

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 charges against him and would defend himself, lawyer Masingo Shela added.

Also among those being tried was a teacher, farmer and journalist.

A judge read the defendants their charges, but at this stage they have not presented their defence.

According to a court document, a total of 53 defendants are on trial, 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.

A separate investigation is being carried out into extrajudicial executions which allegedly took place after the operation, when soldiers were filmed shooting at two suspected unarmed putschists, including one who had jumped into the Congo river to try to escape.

Last March, the Congolese government lifted the moratorium on the death penalty which had been in force since 2003 in the country.

The measure targeted in particular soldiers accused of treason, at a time when the east of the country is in the grip of an armed rebellion.