Police in Hong Kong have come under heavy criticism after a widely-circulated video showed officers tackling a 12-year-old girl to the ground during a pro-democracy protest on Sunday.

The video, posted by the student media group of Hong Kong University of Science and Technology (HKUST), showed the girl walking along a sidewalk when riot police officers stopped her. The girl started running away before the police, armed with batons, helmets, and full-body gear, chased after her and tackled her to the ground. The crowd around them can be heard shouting during the confrontation.

The girl and her brother had been out buying paint for visual arts lessons when they encountered the police, said the girl's mother, identified as Mrs. Ho, speaking on Monday night on public broadcaster RTHK's radio show.

The police force defended its officers' actions, saying in a statement they had deployed "minimum necessary force" in the situation. It said protesters, including the girl, had been intercepted for a stop and search.

"During the interaction, she suddenly ran away in a suspicious manner," the statement said. "Officers, therefore, chased and subdued her with the use of minimum necessary force."

Police said the girl had violated the city's ban on gatherings of more than two people, and added that she was issued a penalty ticket with a fine of $2,000 Hong Kong dollars ($258).

Mrs. Ho said her 12-year-old daughter has suffered bruises from the incident, and that she no longer wished to talk about it or watch the video clip.

"My daughter saw a police officer with a shield and a baton. I can see that he was shouting at my daughter loudly, and it was apparent that my daughter was scared," she told RTHK.

"The question is, is it really necessary for another riot police officer bump into her and push her to the ground from another direction? And use his knee to hold her on the ground. I think it is not necessary," she said. "I was heartbroken when I watched the video again."

In a press conference on Tuesday, the city's leader, Chief Executive Carrie Lam, said it would "not be right" for the Chief Executive to give an opinion on the police operation.

But she said people should "look at the actual circumstances" when evaluating the video clip, and asserted that "every incident and every complaint in terms of the actions taken by law enforcement agencies will be fully investigated."

Ongoing protests

Nearly 300 protesters were arrested on Sunday, according to the police, during one of the largest pro-democracy demonstrations since China imposed a national security law in June.

Hong Kongers were originally scheduled to go to the polls on Sunday, but in July the city's leader postponed legislative elections for a year, citing public health concerns.

Some pro-democracy activists, who had been aiming to win a majority in the city's Legislative Council, accused the government of using the coronavirus pandemic as an excuse -- for fear that pro-government parties could do badly in the vote.

Hong Kong has been in political turmoil since June 2019, when anti-government protests broke out in the city, initially spurred by a controversial extradition bill that was eventually shelved.

Since then, the demonstrations have evolved into a broader protest movement against the city's pro-Beijing government, the Chinese central government, and the police force, which many accuse of excessive force.

Police have consistently argued that their tactics are the result of protesters' violence and disruption, and have strenuously denied wrongdoing and accusations of brutality.