Education Secretary Kevin Yeung on Monday said that the city's schools must make sure they don't have any books that could violate the national security law.

Yeung made the comment after a local newspaper reported that some school libraries have pulled books from their shelves, citing security law concerns.

According to the Ming Pao article, books which have been removed involved topics such as politics and social movements.

Some schools have complained about a lack of specific guidelines from the Education Bureau on vetting reading materials, admitting that this has led to self-censorship, the newspaper reported.

But Yeung said the authorities have always explained clearly to schools that their libraries should only contain books which are suitable for the ages of their students and meet their teaching needs.

He also stressed that schools are responsible for ensuring they don't have books at risk of endangering national security.

If schools encounter any problems, they can reach out to the bureau for assistance, Yeung said.

The education secretary was asked whether he's worried that the national security law has sparked self-censorship in schools, affecting students' learning.

He responded by saying that regardless of the legislation, it is necessary for schools to teach students to think positively and to love their nation. He added that he cannot see any conflict between the requirements laid out under the national security law and school teaching.