PARIS — Civilians are bearing the brunt of the fighting in Syria, Navi Pillay, the United Nations high commissioner for human rights, said Thursday, with 92,901 killings documented there through the end of April, a number that may understate the magnitude of the violence that has devastated cities and villages across the country for 25 months.

“The constant flow of killings continues at shockingly high levels,” Ms. Pillay said in a statement in Geneva, “with more than 5,000 killings documented every month since last July, including a total of just under 27,000 new killings since Dec. 1.”

Ms. Pillay cautioned that the analysis was conservative, and that “the true number of those killed is potentially much higher.”

President Bashar al-Assad’s forces started a bloody crackdown against largely peaceful protesters in March 2011, and defecting soldiers and other government opponents slowly began to take up arms. By fall of that year the conflict had begun devolving, and it is now a bitter civil war with increasingly sectarian overtones. But getting a clear picture of the conflict has been difficult, with few independent journalists able to report from inside the country, while the government and Syrian rebels and activists often issue contradictory reports of battles and massacres.