United Nations (United States) (AFP) - The United States on Tuesday urged Hong Kong to allow freedom of expression as it voiced concern over a ban on the pro-independence party.

Secretary of State Mike Pompeo in a statement said the United States was "concerned" by the ban on the Hong Kong National Party, a first since Britain handed back the trading port 21 years ago to China which assured it would allow semi-autonomy.

"The US supports the freedoms of expression, peaceful assembly, and association," Pompeo said.

"These are core values we share with Hong Kong, and that must be vigorously protected," added Pompeo who is in New York for the annual United Nations General Assembly.

Hong Kong said it was upholding a request from the police to ban the tiny party -- whose core membership is only around a dozen people -- in the interest of preserving public order.

Britain also said it was "concerned" about the move, while stressing that it did not advocate independence for the city.

China voiced "strong dissatisfaction" over foreign criticism, calling on countries not to interfere in Hong Kong or Chinese affairs.