GENEVA — The number of dead in Syria’s civil war more than doubled in the past year to at least 191,000, the United Nations human rights office said Friday. The agency’s chief, Navi Pillay, bluntly criticized Western nations, saying their inaction in the face of the slaughter had “empowered and emboldened” the killers.

In its third report on Syria commissioned by the United Nations, the Human Rights Data Analysis Group identified 191,369 deaths from the start of the conflict in March 2011 to April 2014, more than double the 92,901 deaths cited in the group’s last report, which covered the first two years of the conflict.

“Tragically, it is probably an underestimate of the real total number of people killed during the first three years of this murderous conflict,” Ms. Pillay said in a statement that accompanied the report, which observed that many killings in Syria were undocumented.