Hong Kong police sealed off the Polytechnic University on Sunday after almost two straight days of conflict, in which major roads and a police armoured van were set alight and a police officer was shot with an arrow.
The US has called for Beijing to protect Hong Kong’s freedom amid fears of a violent crackdown.
“We condemn the unjustified use of force and urge all sides to refrain from violence and engage in constructive dialogue,” the senior US official said.
“As the president has said, the United States expects Beijing to honour its commitments under the Sino-British joint declaration and to protect Hong Kong’s freedom, legal system and democratic way of life.”
Officers in Hong Kong said on Monday morning they will consider using live bullets if anti-government protesters continue to use violence against police.
The conflict stems from protests that began in April over a proposed extradition bill, which would have allowed criminal suspects to be sent to mainland China to stand trial.
Although the bill has been withdrawn, the protests have expanded into a wider movement calling for full democracy in the semi-autonomous region and opposing the growth of China’s influence in Hong Kong.
Donald Trump has been largely quiet on the issue since August, when he tweeted about the protests in connection with the ongoing US-China trade war and complained that he was supposedly being “blamed” for the unrest.
Attempts by the US Congress to bring forward legislation in support of the protesters have reportedly faced opposition from the Trump administration, which does not want to anger Beijing while it works on a “Phase One” trade deal with China.
In October, Mr Trump reportedly told Liu He, China’s vice premier, he would keep quiet on the Hong Kong protests in order to make progress on trade.
Additional reporting by Reuters
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