Hong Kong police arrested a seventh person on Wednesday under its new security law in relation to social media posts about commemorating Beijing's 1989 Tiananmen Square crackdown.
The latest arrest comes after an EU spokesperson said law enforcement actions suggest the new legislation "is used to stifle freedom of expression".
Authorities said the 53-year-old woman taken in was suspected of "offences in connection with seditious intention," following the arrests of six people over the same case a day earlier.
Hong Kong's security chief had on Tuesday identified one of those arrested as Chow Hang-tung, a prominent activist who led the now-disbanded group that used to organise annual vigils to mark the Tiananmen Square crackdown.
The group of seven are the first people to be arrested under the "Safeguarding National Security Ordinance" -- commonly referred to as Article 23 -- which Hong Kong enacted in March and penalises sedition with up to seven years in prison.
"The enforcement action is still ongoing and the possibility of further arrests is not ruled out," the National Security Department of the Hong Kong Police said Wednesday.
Hong Kong used to be the only place on Chinese soil where people could openly mourn those who died on June 4, 1989, when the government sent troops and tanks to crush democracy demonstrations in Beijing.
But commemoration has been driven underground in Hong Kong since Beijing's crackdown on dissent, following the huge and sometimes violent pro-democracy protests in 2019.
Before Wednesday's arrest, a spokesperson for the European Union said the law enforcement action "seem to confirm the EU's concerns about the new law and its effect on the rights and freedoms of the people of Hong Kong".
"While we need to assess the details of the individual cases, the arrests suggest that the new law is used to stifle freedom of expression of the people of Hong Kong."
The EU "calls on the Hong Kong authorities to protect the ability of the people of Hong Kong to exercise their rights and freedoms," the spokesperson said.
Passed by an opposition-free legislature, Article 23 became Hong Kong's second national security law, following a Beijing-imposed security law that came into effect in 2020.
The United States, the European Union, Japan and Britain have been among Article 23's strongest critics.
- 'Silencing critique' -
Amnesty International's China director Sarah Brooks called the arrests a "shameful attempt to prohibit people from marking the upcoming anniversary".
The government has weaponised the new security law to "silence critique" despite warnings from United Nations human rights experts, Brooks said.
Chow is already serving a more than 30-month jail sentence over other charges, including "unauthorised assembly" for her attempt to publicly commemorate June 4.
She and two other leaders of the group who organised the vigil are awaiting trial for another national security case, where they are accused of "incitement to subversion".
Authorities connected Chow's latest arrest to a Facebook page called "Chow Hang-tung Club", which in recent weeks has called on the public to write about their experiences related to Tiananmen vigils.
"We hope that all Hongkongers worldwide... who have participated in the candlelight vigils over the past 30 years will write testimonies together," one post read.
The vigil, which once drew tens of thousands to Hong Kong's Victoria Park, has been banned since 2020.
Asked whether it was still legal to mourn Tiananmen, Hong Kong's security chief Chris Tang said Tuesday the key was not the date itself, but "utilising the subject" to incite hatred against the government.
Discussion of the Tiananmen crackdown is highly sensitive for China's communist leadership and commemoration is taboo on the mainland, where many people are unaware of the 1989 events due to wide-reaching censorship.
By Holmes Chan And Xinqi Su