Praising Britain's response to China's controversial new national security law for Hong Kong during a visit to the UK, US Secretary of State Mike Pompeo slammed Beijing's tightening grip on the semi-autonomous city.

The world has seen "Hong Kong's freedoms crushed" and China "bully its neighbors," Pompeo told reporters following talks with British Prime Minister Boris Johnson and Foreign Secretary Dominic Raab in London on Tuesday.

Furthermore, the US' top diplomatic official cast China as an aggressor, saying Beijing had made illegal maritime claims and covered up the COVID-19 outbreak to further its own interests, and describing Chinese Communist Party's behavior towards coronavirus as unforgivable.

"You can't make claims for maritime regions that you have no lawful claim to. You can't threaten countries and bully them in the Himalayas,” Pompeo added, referring to tensions between China and Southeast Asian countries. 

Pompeo offered no evidence of how China had exploited COVID-19.

Read more: Opinion: China is looking to challenge the US

In a sweeping broadside, Pompeo said "we want to see every nation who understands freedom and democracy … to understand this threat being posed by the Chinese Communist Party.”

"We hope we can build out a coalition that understands the threat," he added.

Extradition treaty suspended

The meeting came several hours after London suspended its extradition treaty with Hong Kong and stopped arms sales to the former British colony. The move also comes as China seeks to impose a strict new national security law on the territory. 

Under the new law, crimes such as promoting secession would be punishable by a maximum sentence of life imprisonment. The legislation would also allow for some cases to be tried on mainland China, meaning people extradited to Hong Kong could be tried before judges in mainland courts. 

As a result of the new legislation, Australia, the United States, Canada and the United Kingdom have all suspended extradition agreements with Hong Kong. 

Yuen Long train station anniversary

Meanwhile, hundreds of riot police cordoned off areas of Hong Kong town in a bid to stop small groups of pro-democracy demonstrators marking the one-year anniversary of an attack by armed government supporters in the Yuen Long train station.  

Protesters on Tuesday shouted the popular protest slogan: "Liberate Hong Kong. Revolution of our times," a chant the government has warned might violate new national security laws. 

Pepper spray was used to disperse at least one group of demonstrators and journalists inside a mall in the town of Yuen Long, which lies close to the border with China. 

Authorities reported five people were arrested and hundreds more detained and searched throughout the night. 

The attack inside Yuen Long was a defining moment in last year's pro-democracy protests, which compounded pre-existing animosity towards the police and saw a stark increase in political violence after stick-wielding men set upon a group of protesters returning from a rally in the city. At least 40 people were injured after being beaten.  

Over 9,000 people have been arrested during Hong Kong's pro-democracy rallies in the past year, with some 1,500 charged. 

jlw/nm (AP, AFP, Reuters, dpa)