The agency said the region-wide ban was "based on information that reasonably indicates the use of detainee or prison labor and situations of forced labor," saying it had found examples of debt bondage, restriction of movement, isolation, intimidation and threats, withholding of wages, and abusive living and working conditions.
The State Department estimates that more than 1 million Uyghurs, as well as members of other Muslim minority groups, have been detained in a sprawling network of internment camps in Xinjiang. Accounts of abuse at the camps are numerous.
Beijing has denied accusations of mistreatment, and says it's providing vocational training and helping to deradicalize segments of the population to combat alleged Islamic terrorism and violence.
"CBP will not tolerate the Chinese government's exploitation of modern slavery to import goods into the United States below fair market value," the agency's Acting Commissioner Mark A. Morgan said in a statement.
"Imports made on the cheap by using forced labor hurt American businesses that respect human rights and also expose unsuspecting consumers to unethical purchases," he added.
The ban will be effective at all US ports of entry.
The Trump administration has previously issued import restrictions against companies it accuses of using forced labor in the region, including blocking cotton shipments from the Xinjiang Production and Construction Corps, a major cotton producer.
Eighty-five percent of the cotton produced in China comes from Xinjiang, according to CBP Executive Assistant Commissioner Brenda Smith.
In July, the US issued an advisory warning businesses about the risks of forced labor in Xinjiang, where the "Chinese government continues to execute a campaign of repression targeting the Uyghur people and other ethnic and religious minority groups," CBP said.
Several countries have condemned China's treatment of Uyghurs, but critics have urged the international community to purse a more aggressive regime of sanctions over the issue.
The American move came into effect one day after the British government said it will fine companies which hide connections to the Xinjiang region.
UK Foreign Secretary Dominic Raab on Tuesday announced the new measures, which the Foreign Office says are designed to ensure that British organizations "are not complicit in, nor profiting from, the human rights violations in Xinjiang."
The UK government will also review which British products can be exported to Xinjiang, and issue new guidance "setting out the specific risks faced by companies with links to Xinjiang ... underlining the challenges of effective due diligence there."