Hong Kong pro-democracy media outlet Stand News shut down on Wednesday after police raided its office, froze its assets and arrested senior staff on suspected “seditious publication” offences, in the latest crackdown on the city’s media.

Stand News, set up in 2014 as a non-profit, was the most prominent remaining pro-democracy publication in Hong Kong after a national security investigation this year led to the closure of jailed tycoon Jimmy Lai’s Apple Daily tabloid.

The raid raises more concerns about press freedom in the former British colony, which returned to Chinese rule in 1997 with the promise that a wide range of individual rights would be protected, media advocacy groups said.

“Stand News is now stopping operations,” the publication said on Facebook, adding all employees had been dismissed.

The head of a police national security department, Steve Li, told reporters Stand News had published news and commentary inciting hatred against authorities.

Li said police seized assets worth HK$61 million ($7.82 million) as well as computers, phones and journalistic materials, and that he did not rule out further arrests.

“We are not targeting reporters. We are targeting national security offences,” Li said.

Police said 200 officers searched the Stand News office and three men and four women, aged 34-73, were arrested on suspicion of “conspiracy to publish seditious publications”.

Police did not identify them but media said four former members of the Stand News board were arrested — former democratic legislator Margaret Ng, pop singer Denise Ho, Chow Tat-chi and Christine Fang — as well as former chief editor Chung Pui-kuen and acting chief editor Patrick Lam.

Chung’s wife, Chan Pui-man, formerly with Apple Daily, was re-arrested in prison, media said. Reuters could not reach those arrested or their legal representatives.

Ronson Chan, Stand News deputy assignment editor and the head of the Hong Kong Journalists Association, was not among those arrested but said police confiscated his computer, mobile, tablet, press pass and bank records during a search of his home.

“Stand News has always reported news professionally,” Chan told reporters.

Hong Kong chief secretary John Lee told reporters he supported the police action.

“Anybody who attempts to make use of media work as a tool to pursue their political purpose or other interests countering the law, particularly offences that endanger national security, they are the evil element that damage press freedom,” Lee said.