Britain has suspended its extradition treaty with Hong Kong in what Prime Minister Boris Johnson has called a "tough" but balanced response to China's imposition of a new security law on the territory.
Foreign Secretary Dominic Raab told parliament the national security law was a "clear and serious violation" of China's 1984 joint commitment with Britain to uphold basic freedoms in Hong Kong.
As a result, he said, the government would suspend the extradition treaty and extend an arms embargo to Hong Kong that has applied to mainland China since 1989, when troops killed hundreds of protesters as they quashed a student-led democracy movement in Beijing.
Mr Raab said the measures against China were "a necessary and proportionate response to this new national security legislation".
Despite the diplomatic friction, Britain "wants a positive relationship with China," he added.
"There is enormous scope for positive, constructive engagement," Mr Raab said.
"But, as we strive for that positive relationship, we are also clear-sighted about the challenges that lie ahead."
Mr Raab added that Britain is watching to see how China enforces the security law and is engaged with international partners in "a concerted dialogue about how we should best respond to events in Hong Kong".
US Secretary of State Mike Pompeo was scheduled to discuss Hong Kong and China with Raab in London on Tuesday.
Australia and Canada suspended their extradition agreements with Hong Kong earlier this month amid similar concerns.
Speaking ahead of Mr Raab's announcement, Chinese Foreign Ministry spokesman Wang Wenbin accused the British government of seeking to "flagrantly interfere in China's domestic affairs" in Hong Kong.
Britain handed control of the territory to China in 1997 after more than 150 years of colonial rule.
Mr Wang defended the security law, claiming it ensures the "steady and sustained implementation of 'one country, two systems' in Hong Kong".
"We urge the UK to stop going further down the wrong path to avoid greater damage to China-UK relations," he said.
