Fifty-one people, including three US citizens, are on trial over the incident, which began in the early hours of May 19 when armed men attacked the home of the DRC's Economy Minister Vital Kamerhe.

The group then went to a building housing President Felix Tshisekedi's offices, brandishing flags of Zaire, the country's name under ex-dictator Mobutu Sese Seko, who was overthrown in 1997.

Shots were heard near the building, several sources said at the time.

An army spokesman later announced on national TV that defence and security forces had stopped "an attempted coup d'etat".

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.

Three days ago, military prosecutor Lieutenant Colonel Innocent Radjabu urged judges to sentence to death all but one of the 51 defendants.

"We plead not guilty," Richard Bondo, a lawyer for US citizen Benjamin Zalman-Polun, told the court on Friday, calling for the detainees to be released.

The three Americans on trial at the Kinshasa military court include Malanga's son Marcel Malanga.

Tyler Thompson, another of the American defendants, told the court last month that he had been "forced" into participating, echoing the two other US citizens facing the same charge.

Zalman-Polun said he was "kidnapped" and "forced" into taking part.

The defendants also include a Belgian, a Briton and a Canadian who are all naturalised Congolese.

The trial began on June 7 in Ndolo military prison, where all the defendants are being held.

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