The United States is withdrawing from the UN Human Rights Council as the organisation is "not worthy of its name", President Donald Trump's UN envoy has said.
Nikki Haley said a year ago she made clear the US would stay in the council only if "essential reforms were achieved", and on Tuesday said it was clear those calls for change were not heeded.
It comes as the United States faces intense criticism for detaining children separated from their immigrant parents at the US-Mexico border.
UN High Commissioner for Human Rights Zeid Ra'ad al-Hussein on Monday called on Washington to halt its "unconscionable" policy.
Haley blasted the membership of countries like China, Cuba and Venezuela that are themselves accused of rights violations.
She say the council also has a "chronic bias against Israel". But Haley said that if the council does reform, the United States "would be happy to rejoin".
Haley announced the withdrawal at the State Department alongside US secretary of state Mike Pompeo.
The United States is half-way through a three-year term on the main UN rights body and had long threatened to quit if it was not reformed.
UK Foreign Secretary Boris Johnson said the decision was "regrettable".
UK Foreign Secretary Boris Johnson said: "The United States' decision to withdraw from the Human Rights Council is regrettable.
"We've made no secret of the fact that the UK wants to see reform of the Human Rights Council, but we are committed to working to strengthen the council from within.
"Britain's support for the Human Rights Council remains steadfast. It is the best tool the international community has to address impunity in an imperfect world and to advance many of our international goals.
"That's why we will continue to support and champion it."
Ken Roth, executive director of the Human Rights Watch, said: "The UN Human Rights Council has played an important role in such countries as North Korea, Syria, Myanmar and South Sudan, but all Trump seems to care about is defending Israel."
When the Human Rights Council was created in 2006, US President George W Bush's administration shunned the body.
Then under President Barack Obama, the United States was elected to the body for a maximum two consecutive terms on the council by the UN General Assembly.
After a year off, Washington was re-elected in 2016 for its current third term.
In March 2011, the UN General Assembly unanimously suspended Libya's membership in the council because of violence against protesters by forces loyal to Libyan leader Muammar Gaddafi. But U.N. officials said no member has withdrawn.
Haley said a year ago that Washington was reviewing its membership and called for reform and elimination of a "chronic anti-Israel bias".
The body has a permanent standing agenda item on suspected violations committed by Israel in the occupied Palestinian territories that Washington wants removed.