The United Nations’ human rights office says it is “deeply concerned” by US President Donald Trump’s pardons of four former government contractors convicted for a 2007 massacre in Baghdad that left more a dozen Iraqi civilians dead.

Pardons for the four former US service members – Nicholas Slatten, Paul Slough, Evan Liberty and Dustin Heard – were among 15 that were announced by Mr Trump on Tuesday.

Supporters of the former contractors at Blackwater Worldwide had lobbied for pardons, arguing that the men had been excessively punished in an investigation and prosecution they said was tainted by problems and in which exculpatory evidence was withheld.

“These four individuals were given sentences ranging from 12 years to life imprisonment, including on charges of first-degree murder,” UN human rights office spokeswoman Marta Hurtado said in a statement released in Geneva.

“Pardoning them contributes to impunity and has the effect of emboldening others to commit such crimes in the future.”

She said that “victims of gross human rights violations and serious violations of international humanitarian law also have the right to a remedy,” which includes a right to “see perpetrators serve punishments proportionate to the seriousness of their conduct”.

Among others pardoned by Mr Trump was George Papadopoulos, a former campaign aide who pleaded guilty as part of the investigation into Russian meddling in the 2016 presidential election, and former Congressmen Chris Collins and Duncan Hunter.