HONG KONG (AP) - Hong Kong's leading security figure stated on Thursday that booksellers bear the duty to verify that the books they offer do not compromise national security. This comes one day after authorities detained five people associated with a pair of bookstores.

The police action on Wednesday marked the third instance of targeting independent bookstores in just four months. Observers have expressed worries about the city's expressive freedoms amid what appears to be an ambiguous boundary. Two of those detained were observed being released on bail Friday morning.

During a Thursday briefing at the legislative building, Security Secretary Chris Tang informed reporters that regulations are straightforward.

"Booksellers hold the obligation to confirm that the publications they distribute will not jeopardize national security," he remarked. "This parallels the requirement when vending food, where one must guarantee it causes no illness and contains nothing poisonous or prohibited."

When questioned about creating a catalog of prohibited books, Tang indicated it would hinder precise enforcement against works "meant to damage the nation."

"We refuse to allow offenders to evade accountability in such a manner," he added.

Police searched Have A Nice Stay, established by former journalists, and the established Greenfield Book Store on Wednesday. The five arrested individuals face allegations of exhibiting seditious content and distributing seditious materials, according to authorities.

A police release claimed the materials incited animosity toward the local administration, courts, and police forces.

Have A Nice Stay had previously declared its closure on Aug. 30, citing economic challenges and the unclear boundary in a social media announcement.

The store noted its inability to review every book and its limited capacity to identify "problematic" titles.

Back in March, officers detained the proprietor and employees of the independent Book Punch store, reportedly for offering seditious publications, including a biography of former pro-democracy media figure Jimmy Lai, who received a 20-year sentence in his national security case.

In June, Hong Kong police took two booksellers into custody over suspicions of vending seditious items and accepting support from overseas political entities.

Taiwan's President Lai Ching-te, on the self-ruled democratic island claimed by China, highlighted in a Facebook update the pressures on Hong Kong's freedoms of speech and publishing.

"Independent bookstores play a crucial role in protecting free ideas," he stated.

Liang Wen-chieh, deputy head of Taiwan's Mainland Affairs Council, informed journalists that certain Taiwanese publishers have engaged in self-censorship regarding their book selections for a Hong Kong book event.