US defendants Tyler Thompson, Marcel Malanga and Benjamin Zalman-Polun have faced court. [Source: AP]

Three US citizens are among 37 defendants sentenced to death by a military court for their role in a May failed coup in the Democratic Republic of Congo.

Armed men briefly occupied an office of the presidency in the capital Kinshasa on May 19 before their leader, US-based DR Congolese politician Christian Malanga, was killed by security forces.

His son, Marcel Malanga, was among the US citizens on trial, along with Marcel’s friend, Tyler Thompson, who played high school football with him in Utah.

Both are in their 20s.

The third US defendant, Benjamin Zalman-Polun, was a business associate of Christian Malanga.

All three were found guilty of criminal conspiracy, terrorism and other charges, and sentenced to death in a ruling read on live TV.

Malanga had previously told the court that his father had threatened to kill him unless he participated.

He also told the court it was his first time visiting DR Congo at the invitation of his father, whom he had not seen in years.

The three are among 50 people, including US, UK, Canadian, Belgian and DR Congolese citizens standing trial following the failed coup.

A total of 37 defendants were sentenced to death.

The verdict was read out under a tent in the yard of Ndolo military prison on the outskirts of Kinshasa.

The defendants were seated in front of the judge, wearing blue and yellow prison-issued tops.

The trial began in July.

US State Department spokesman Matthew Miller said embassy staff had attended the proceedings and would continue to follow developments closely.

“We understand that the legal process in the DRC allows for defendants to appeal the court’s decision,” he told a briefing.

The 37 defendants include Belgian-Congolese citizen Jean-Jacques Wondo.

Wondo’s family released video messages addressed to DR Congo President Félix Tshisekedi ahead of the trial to ask for his release.

“I beg you, intervene, he is innocent,” Nathalie Kayembe Wondo, his wife, said in the message.

Marcel Malanga’s mother Brittney Sawyer has previously said her son is innocent.

Thompson’s stepmother, Miranda Thompson, has previously said her stepson travelled to DR Congo on a holiday to explore the world.

Thompson is feeling lonely and isolated in prison, according to the fundraising site that his family set up to support his defence.