China and the U.S. traded barbs with one another Friday as demonstrators in Hong Kong began a three-day protest at the city’s airport.

The State Department slammed the Chinese government Thursday, accusing it behaving like a “thuggish regime” after a state newspaper published personal information of an American diplomat in Hong Kong who reportedly spoke with supposed “Hong Kong independence” activists.

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“I don’t think that leaking an American diplomat’s private information, pictures, names of their children – I don’t think that is a formal protest, that is what a thuggish regime would do,” State Department spokeswoman Morgan Ortagus said at a news briefing in Washington on Thursday.

This prompted China on Friday to attack the U.S. for “gangster logic” and accused the U.S. of meddling in Hong Kong affairs.

“The spokesperson at the commissioner’s office denounced the claim as a blatant slander against China, which has confounded right with wrong and again exposed U.S. gangster logic and hegemonic thinking. China deplores and firmly opposes the remarks,” said the Office of the Commissioner of the Ministry of Foreign Affairs in Hong Kong.

The insults came as demonstrations at the airport and across the city are kicking off. Signs held by protesters in the airport’s arrival hall included those saying “There are no rioters, only tyranny.”

Activists also left pamphlets stacked in piles that warned visitors of the heavy use of tear gas by police. Officers said 800 canisters were used during protests on Monday alone, and journalists and protesters say many suffered skin irritation and internal injuries as a result.

The airport appears to be operating normally, extra identification checks were put in place for both travelers and staff, and airlines were advising passengers to arrive earlier than usual for check-in.

A similar airport protest last month ended peacefully. Authorities didn’t indicate that there’s a plan to use force to end the unauthorized demonstration.

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“The police will closely monitor the situation this weekend and make respective deployment as necessary. It will be dependent on what happens at the time,” said officer Vasco Williams, who is operations superintendent for the district of New Territories North.

Hong Kong has been reeling from frequent protests ever since the city’s government, which is supposed to be separate from communist Chinese influence, introduced an extradition bill that critics say would threaten the liberties awarded to the city as people could be extradited to face the law in the mainland China.

The bill was temporarily suspended following protests, however, the demonstrations morphed into demands for greater freedoms and against the excessive use of force by the authorities.

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Hong Kong is a former British colony that is now part of China but enjoys autonomy thanks to the “one country, two systems” approach.

The Associated Press contributed to this report.