The High Court has dismissed an application for early release by a University of Hong Kong student jailed for praising a knife attack on a police officer three years ago.

Four university students were jailed for two years last October for incitement to wound with intent after passing a motion mourning Leung Kin-fai, who killed himself after stabbing a police officer in 2021. The sentences were later reduced to 15 months by the Court of Appeal.

One of the four, Kinson Cheung, applied for habeas corpus – a writ made to a court so it can assess whether a detention is lawful – and asked to be given a one-third reduction in his sentence for good behaviour.

In a hearing on Tuesday, the Correctional Services Department (CSD) submitted documents from the Committee for Safeguarding National Security chaired by the chief executive, stating that reducing Cheung's sentence further would be detrimental to national security.

High Court judge Anna Lai accepted the CSD's submissions and rejected Cheung's bid for early release.

She also threw out the habeas corpus application.

Responding to questions on the case before the court decision, Chief Executive John Lee said certificates to certify whether an act involves national security are issued in accordance with the law.

"All procedures for national security cases will be done in strict accordance with legal procedure and the relevant laws. But I want to repeat again, we will deal with national security offences seriously and we will enforce the law without hesitation because national security offences are serious," he said.