U.S. national security adviser Robert O’Brien said on Friday that China was perpetrating "something close to" a genocide with its treatment of Muslims in its Xinjiang region.
He made the comments during an online event hosted by the Aspen institute.
"They are bullying Taiwan again. They've taken over Hong Kong, lock, stop and barrel. Tibet remains out there. If not a genocide, something close to it going on in Xinjiang so the Chinese are very very assertive, very aggressive now."
The United States has denounced China's treatment of Uighur and other minority Muslims in the region and imposed sanctions on officials it blames for abuses.
But it has not so far termed Beijing's actions genocide, a designation that would have significant legal implications and require stronger action against China.
The United Nations estimates that more than a million Muslims have been detained in Xinjiang and activists say crimes against humanity and genocide are taking place there.
China has denied any abuses and says its camps in the region provide vocational training and help fight extremism.
O'Brien on Friday referred to seizures by U.S. customs of quote "massive numbers" of hair products made with human hair from Xinjiang.
"The Chinese are literally shaving the heads of Uighur women and making hair products and sending them to the United States," he said
U.S. Secretary of State Mike Pompeo in June labeled as "shocking" and "disturbing" reports that China was using forced sterilization, forced abortion and coercive family planning against Muslims in Xinjiang.