The Trump administration has characterised the repression of Muslim Uighurs in China’s Xinjiang province as genocide, in a last-minute move that will increase pressure on US president-elect Joe Biden to address the claims.

Mike Pompeo, US secretary of state, said: “I believe this genocide is ongoing and that we are witnessing the systematic attempt to destroy Uighurs by the Chinese party-state.”

Mr Pompeo took the step in his final full day in office, accusing China of crimes against humanity, including forced sterilisations and torturing some of the “more than a million” civilians he said were detained under the direction of the Chinese Communist party.

He called on “all appropriate multilateral and relevant juridical bodies to join the United States in our effort to promote accountability for those responsible for these atrocities”. He said the US state department would continue to investigate and make evidence available to appropriate authorities and the international community.

The Trump administration has repeatedly moved to censure Chinese officials over the alleged treatment of Uighurs but had stopped short of designating it as a genocide, a term first legally applied to the mass planned murder of Jews during the Holocaust.

The incoming Biden team had already referred to the oppression of Uighurs as genocide during the presidential campaign and had called on Donald Trump to act, saying Mr Biden stood against it “in the strongest terms”.

Senior state department officials had considered taking such a step for more than a year but had stopped short owing to political considerations at higher levels, according to several people briefed on the matter.

Ben Sasse, a Republican senator who sits on the Senate select committee on intelligence, said the decision was “good and right, but it’s late”.

“The United States isn’t taking the Uyghur genocide seriously,” he added. “A lot of folks in the Trump Administration wanted to talk about China primarily in terms of a trade deficit, and a lot of folks in the Biden Administration want to talk about China as merely a competitor.”

Sam Brownback, ambassador at large for international religious freedom, has spent years campaigning on behalf of Uighurs during his stint in the administration, and Uighurs have regularly featured at events the Trump administration has held in support of religious freedom.

Mr Pompeo called on China to release all arbitrarily detained persons “and abolish its system of internment, detention camps, house arrest and forced labour”.

He also called for Beijing to cease coercive population control measures, which he said included forced sterilisations, forced abortion, forced birth control and the removal of children from their families.

China regularly denies mistreatment of Uighurs and has sought to limit scope for discussions about human rights at the UN.

Sophie Richardson at Human Rights Watch, whose campaigners have documented abuses against Uighurs for 25 years, welcomed the move but added a multilateral approach was needed. Mr Trump withdrew the US from the UN Human Rights Council.

Richard Gowan, a UN expert at International Crisis Group, said that although the US had worked closely with European counterparts to raise the issue of the Uighurs at the UN in the past two years, many of the countries that have sided with the US against China over Xinjiang would find this last-minute intervention “unhelpful”.

UN secretary-general António Guterres will probably come under pressure to affirm the US position that the repression amounted to genocide, Mr Gowan said, which could be difficult because Mr Guterres will need the backing of all five permanent members of the UN — which includes China — to secure reappointment later this year.

Mr Biden’s team has vowed to harden its approach to China with bipartisan support, although it also plans to seek co-operation in some areas such as climate change.

Antony Blinken, Mr Biden’s pick as secretary of state who is due to appear in a confirmation hearing before the US Senate on Monday, is a staunch advocate of human rights.