LIMA, Peru — United Nations human rights experts on Thursday condemned the decision to grant a medical pardon to Alberto Fujimori, the former president of Peru who had been serving a 25-year sentence for extrajudicial killings and other grave crimes.

The pardon, announced on Sunday by President Pedro Pablo Kuczynski, set off an outcry that has roiled this Andean nation. Mr. Fujimori, who was in office from 1990 to 2000, remains deeply divisive, respected in some quarters for his economic reforms and his crackdown on two violent insurgencies, but reviled by others for his strongman tactics and for military-backed atrocities during his tenure.

“The presidential pardon granted to Alberto Fujimori on politically motivated grounds undermines the work of the Peruvian judiciary and the international community to achieve justice,” the experts said in a statement released by the office of the United Nations high commissioner for human rights. “We are appalled by this decision. It is a slap in the face for the victims and witnesses whose tireless commitment brought him to justice.”

The experts — Agnès Callamard, special rapporteur on extrajudicial killings; Pablo de Greiff, special rapporteur on truth, justice and reparations; and a working group on enforced or involuntary disappearances — added: “It is also a major setback for the rule of law in Peru: A humanitarian pardon has been granted to someone convicted of serious crimes after a fair trial, whose guilt is not in question and who does not meet the legal requirements for a pardon.”