Armed men attacked the home of Economy Minister Vital Kamerhe in the early hours of May 19 before moving onto the nearby Palais de la Nation that houses President Felix Tshisekedi's offices.

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

The trial began at around 11:40 am local time (1040 GMT) before a military court held inside the Ndolo military prison in the capital Kinshasa, AFP reporters saw.

The accused, who also include four women, were dressed in blue and yellow prison uniforms.

They took their place in a large tent in the prison courtyard where hearings take place.

Western diplomats were present in addition to journalists and lawyers.

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.

Ekenge said the attackers were made up of "several nationalities" and that around 40 were arrested, with another four -- including Malanga -- killed.

The motive behind the incident remains unclear, but the government condemned it as an "attempted destabilisation of the institutions".

A court document shows that 53 defendants are being tried, including Christian Malanga, even though he is dead.

His son, who is American, as well as two other US citizens are also being tried.

At least one Congolese man who is a naturalised Belgian is also among the defendants.

The charges in the case are "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 allegedly committed by soldiers after the operation.