Three Americans convicted for their role in a failed coup in Democratic Republic of Congo last year have had their death sentences commuted to life imprisonment, the presidency has said.

They were among 37 people sentenced to death last September by a military court.

The three were accused of leading an attack on both the presidential palace and the home of an ally of President Félix Tshisekedi last May.

The overturning of the sentences comes ahead of a visit to DR Congo by the newly appointed US senior adviser for Africa, Massad Boulos.

Boulos, father-in-law to President Donald Trump’s daughter, Tiffany, is expected to arrive in the Congolese capital, Kinshasa, on Thursday on a trip that will also take him to Rwanda, Kenya and Uganda.

The US has not declared the three Americans to be wrongfully jailed in DR Congo but the State Department said previously there had been talks between the countries over the matter.

The three were convicted of criminal conspiracy, terrorism and other charges, which they denied.

The suspected leader of the plot, Christian Malanga, a US national of Congolese origin, was killed during the attack, along with five others.

In total 51 people were tried in a military court, with hearings broadcast on national TV and radio.

Fourteen people were acquitted and freed, with the court finding they had no connection to the attack.

Death sentences have not been carried out in DR Congo for roughly two decades and convicts who receive the penalty usually serve life imprisonment instead.

The government lifted this moratorium in March this year, citing the need to remove “traitors” from the nation’s dysfunctional army. However, no death penalties have been carried out since.

On Tuesday, President Tshisekedi signed orders to commute the Americans’ death sentences, his spokesperson Tina Salama said in a televised statement.

The three – Marcel Malanga Malu, Tylor Thomson and Zalman Polun Benjamin – were granted “individual clemency” by the president, according to Salama.

Ckiness Ciamba, one of Malanga’s lawyers, told the Reuters news agency that the “presidential pardon is a first step that promises major changes in the future”.

Jean-Jacques Wondo, a dual Congolese and Belgian citizen who was also sentenced to death, was in February transferred to Belgium because of ill-health. It is unclear if the Americans could also be sent home to serve out their sentences.

It is also not clear if the other convicts, who include a Briton, a Belgian and a Canadian national, will also have their sentences commuted.

The attempted coup began in Kinshasa in the early hours of 19 May, when armed men first attacked parliamentary speaker Vital Kamerhe’s home, before heading to the president’s official residence in the capital.

Witnesses say a group of about 20 assailants in army uniform attacked the palace and an exchange of gunfire followed.

Additional reporting by Emery Makumeno in Kinshasa & Natasha Booty in London