“The State Department is reviewing that now because all of the procedures were not followed,” Linda Thomas-Greenfield told the US Senate Foreign Relations Committee.

“They’re looking to make sure that they are followed to ensure that that designation is held.”

Former Secretary of State Mike Pompeo made the move last week, one day before Biden took office, “after careful examination of the available facts”, accusing the Chinese Communist Party of crimes against humanity targeting the Uighurs and other Muslim minorities.

China has been widely condemned for its complexes in Xinjiang, which it describes as “vocational training centres” to stamp out extremism. It denies accusations of abuse.

Later on Wednesday, a bipartisan group of US senators said it had reintroduced legislation intended to bar any goods made with forced labour in Xinjiang from entering the US.

The rare American genocide determination came after Congress passed legislation on Dec 27 requiring the US administration to determine within 90 days whether China had committed crimes against humanity or genocide.

Biden’s secretary of state, Antony Blinken, told the foreign relations panel during his confirmation hearing last week that he agreed with the genocide declaration.

China’s embassy in Washington had responded to Pompeo’s announcement, saying: “The so-called ‘genocide’ in Xinjiang is simply a lie. It is a farce used to discredit China.” It rejected the US declaration as a “gross interference in China’s internal affairs”.

The Uighur forced-labour bill passed the House of Representatives by a huge margin last year, but had to be introduced again because it did not pass the Senate and become law before the new Congress was seated this month.