The director of Human Rights Watch was barred from entering Hong Kong to present a key report, because of what China called his organisation’s role in supporting the months-long protests in the city.

Kenneth Roth posted a video on Twitter from Hong Kong’s international airport late on Sunday, saying he was being put back on a flight to the US because of an unspecified “immigration problem”, with officials refusing to provide further information.

But at a news conference on Monday, the Chinese foreign ministry spokesperson Geng Shuang lashed out at Mr Roth’s New York-based organisation, accusing Human Rights Watch of instigating “anti-China activists” to “engage in radical violent crimes, and incite separatist activities hyping Hong Kong independence”.

Hong Kong citizens have been taking to the streets, sometimes in their millions, in mass demonstrations since June last year. The movement began in protest against a new extradition law, which was eventually dropped, but snowballed into an expression of broader anger at Beijing’s rule.

According to Mr Geng, however, it was in fact groups such as Human Rights Watch who were to blame for the crisis. International NGOs, he said, “deserve sanctions and must pay a price”.

Mr Roth had been travelling to Hong Kong to launch his organisation’s annual World Report, which he said was going to focus particularly on China’s efforts to “deliberately undermine the international human rights system… not simply suppress[ing] rights of people at home but also undermin[ing] the ability of anybody else to hold China to human rights standards”.

Experts had previously called the choice to launch the report in Hong Kong itself significant. It will now be unveiled at a press conference in New York instead, Mr Roth said.

In a series of tweets upon his return to the US, Mr Roth said he had previously travelled freely to Hong Kong, including as recently as April 2018 when he released a report on gender discrimination in the Chinese job market.

“Sadly this episode is just the latest evidence that the Chinese government is doing everything it can to undermine the enforcement of international human rights standards,” he said.

Sophie Richardson, director of Human Rights Watch’s China programme, told The Independent, that Beijing’s statement on Monday “raises questions about whether Hong Kong actually has any autonomy on these matters”.

She described blaming foreign interference as “one of the authoritarian’s favourite dodges”. “These remarks are especially insulting to the millions of people across Hong Kong who have - of their own volition - come out week after week, in the heat and the pouring rain, to peacefully demonstrate for their rights,” she said.

Meanwhile, an incident involving graffiti and Denmark’s iconic “Little Mermaid” statue on Monday demonstrated once again the extent to which the Hong Kong protest crisis is playing out on the international stage.

Police in Copenhagen were searching for clues after the country’s most famous landmark was adorned with red writing that read: “Free Hong Kong”.

The bronze statue is said to be especially popular with Chinese visitors to Denmark. It depicts the little mermaid from 19th-century Danish author Hans Christian Andersen's tale of the same name, perched on a rock by a waterside promenade.

More than one million tourists visit the Little Mermaid every year, and it has been defaced and damaged several times, twice suffering decapitation.

It is not the first time an incident involving Hong Kong-related vandalism has played out far from the city where the unrest is taking place.