The US has called for the UK and countries around the world to form a coalition, aimed at persuading China to change course as tensions between Beijing and the West rise.
US Secretary of State Mike Pompeo welcomed recent steps taken by the UK over China, including Monday's announcement on extending its arms embargo to Hong Kong.
He also praised the UK's move to strip Chinese tech giant Huawei's equipment from its 5G network by 2027, describing it as a "good decision".
Speaking at a press conference in Lancaster House in London following talks with his British counterpart, Mr Pompeo said "we have seen Hong Kong's freedoms crushed" and "watched the CCP [Chinese Communist Party] bully its neighbours".
"I want to take this opportunity to congratulate the British Government for its principled response to these challenges," he said.
"We support those sovereign choices, we think 'well done'."
Foreign Secretary Dominic Raab said he and Mr Pompeo had both discussed their "serious concerns" over the sitiuation in Hong Kong and about raising the issue of China's actions at "G7 level".
Mr Raab denied the UK was being "strong-armed" by the US into its position over China, while Mr Pompeo suggested countries, including Britain, need to do more to counter the increasingly assertive country.
"We think that the entire world needs to work together to ensure that every country – including China – behaves in the international system in ways that are appropriate and consistent with the international order," Mr Pompeo said.
"You can’t go make claims for maritime regions that you have no lawful claim to. You can’t threaten countries and bully them in the Himalayas.
"You can’t engage in cover-ups and co-opt international institutions like the World Health Organisation."
Downing Street insisted it had taken a "reasonable" approach to Beijing after China’s embassy in the UK warned Britain would "bear the consequences" over its moves on Monday.
The Prime Minister’s official spokesman said on Tuesday it was a "reasonable and proportionate response to China’s failure to live up to its international obligations with respect to Hong Kong".
The UK has accused China of breaking the terms of an international treaty by imposing the national security law, which the Government believes undermines some of the autonomy Hong Kong has previously enjoyed.
Earlier on Tuesday, Boris Johnson and Mr Pompeo met and discussed the situation in China and the need for members of the Five Eyes security alliance to work on the "technologies of the future".
They also spoke about the situation in Iran, the Middle East and their "commitment to negotiate a strong UK-US free trade agreement".
A spokesman for the Chinese Embassy in London called on the UK to "immediately stop interfering in Hong Kong affairs, which are China’s internal affairs, in any form".
"Now the UK side has gone even further down the wrong road in disregard of China’s solemn position and repeated representations,” the spokesman said in a statement.
Last week, reports emerged that Royal Navy aircraft carrier HMS Queen Elizabeth could be sent to the Far East on her first deployment to counter growing Chinese assertivenes.
The Ministry of Defence (MOD) said "no decision" has been made, although a senior Navy officer also suggested it could be sent there.
The Chinese Ambassador to the UK warned basing an aircraft carrier in the region would be a "very dangerous move".