The US on Thursday denounced China as a “thuggish regime” after a state newspaper published the name and photo of a US diplomat talking to activists.
China has dismissed the attacks as “gangster logic”, and has repeatedly accused the US of interfering in Hong Kong.
The accusations come as activists gather at Hong Kong’s airport for three days of unauthorised protests.
Demonstrators dressed in black sat in the arrivals hall waving banners to raise awareness among international visitors.
Hong Kong has seen weeks of demonstrations, beginning with anger at an extradition bill and morphing into demands for greater freedoms.
The former British colony is part of China but enjoys more autonomy. It has a free press and judicial independence under the “one country, two systems” approach – freedoms activists fear are being increasingly eroded.
They have called for an independent inquiry into alleged police brutality during the protests, the complete withdrawal of the controversial extradition bill, and the resignation of Hong Kong’s leader Carrie Lam.
On Thursday, China asked the US to explain reports its diplomats were in contact with Hong Kong protest leaders.
Ta Kung Pao newspaper – a pro-Beijing publication – had published a photo of US diplomat Julie Eadeh meeting student leaders at a hotel, under the headline “Foreign Forces Intervene”.
China has repeatedly accused the US of meddling in Hong Kong’s recent political crisis.
The US rejected the accusation, saying its diplomats meet wide a range of people – including from the government and from businesses – and criticised the report.
“I don’t think that is a formal protest, that is what a thuggish regime would do,” spokeswoman Morgan Ortagus told reporters, adding it was “not how a responsible nation would behave”.
China in turn has dismissed “gangster logic” from the US, and said the country should stop interfering in its affairs.
The feud comes as demonstrators gathered at Hong Kong airport for three days of protests.
Activists waved banners written in different languages denouncing Carrie Lam and the police, and handed out leaflets with artwork explaining the recent protests.
Authorities are so far tolerating the peaceful rally, which have not overly disrupted passengers. There are as yet no police at the scene.
“It will be a peaceful protest as long as the police do not show up,” one demonstrator told Reuters news agency.