GENEVA (Reuters) – Britain said on Tuesday that China’s plan to impose national security legislation on Hong Kong would undermine the autonomy in the former British colony and could threaten its rights and freedoms.

Britain returned Hong Kong to Chinese rule in 1997 with the guarantee of freedoms, such as an independent judiciary and right to protest, for 50 years.

“The imposition of the proposed law lies in direct conflict with China’s international obligations under the Joint Declaration, a treaty agreed by the UK and China and registered with the United Nations,” Julian Braithwaite, Britain’s ambassador to the U.N. in Geneva, told the Human Rights Council.

He urged China to engage with Hong Kong’s people, institutions, and judiciary to “ensure it maintains Hong Kong’s high degree of autonomy and rights and freedoms”.

There was no immediate reaction by China’s delegation to the 47-member state forum, which is holding a session this week.

Pang Kwang Hyok, deputy ambassador at North Korea’s mission, voiced concern at “certain countries’ attempt to use Hong Kong-related issues to interfere in China’s domestic affairs”. Hong Kong was “an inseparable part” where China’s sovereignty is exercised and its constitution is applied, he said.

Hong Kong’s national security legislation would not punish people retroactively, a senior Chinese official said on Monday, touching on a key question raised by local residents, diplomats and foreign investors over the controversial law.

Beijing last month moved to directly impose the legislation on Hong Kong in a bid to tackle secession, subversion and foreign interference in the city and financial hub.

Hong Kong was rocked by months of sometimes violent anti-China, pro-democracy unrest last year, with protesters angry at what they see as meddling by Communist Party rulers in Beijing in Hong Kong’s affairs.

China denies interfering and blames Britain and the United States for fomenting trouble.