The US has pulled out of the United Nations Human Rights Council, calling it a "cesspool of political bias".
Nikki Haley, the US envoy to the UN, said it was a "hypocritical" body that "makes a mockery of human rights".
Formed in 2006, the Geneva-based council has faced criticism in the past for allowing member countries with questionable human rights records.
But activists said the US move could hurt efforts to monitor and address human rights abuses around the world.
Announcing the decision to quit the council, Ms Haley described the council as a "hypocritical and self-serving organisation" that displayed "unending hostility towards Israel".
She was speaking alongside US Secretary of State Mike Pompeo, who denounced the council as "a protector of human rights abusers".
The UN Secretary-General António Guterres responded to the US decision to quit the council by saying he would have "much preferred" the US to remain a member.
The UN's human rights chief Zeid Ra'ad al-Hussein called the US withdrawal "disappointing, if not really surprising, news". Israel, meanwhile, praised the decision.