Hong Kong’s national security police have arrested a man on suspicion of sedition after he allegedly reposted a video clip of a protest song linked to 2019’s social unrest being played at a rugby match involving the city’s team in Incheon earlier this month and expressed gratitude to the South Korean authorities.

Officers searched the 42-year-old courier’s home and office after he was arrested in New Territories on Monday, a force spokesman said.

A force insider said the man had allegedly disseminated seditious messages, including “delivering mail is no longer my duty. The most important thing to do now is to fight for Hong Kong”, since last year via his social media accounts.

He was also said to have advocated “self-training for black-clad violence”, referring to the protests during the 2019 social unrest.

And he appealed to people who were opposed to the government’s anti-pandemic policy to resist, the source added.

The police source said the man had reposted the viral video clip showing Asia Rugby – the organisers of the tournament in Incheon – playing the protest song “Glory to Hong Kong” rather than “March of the Volunteers” as the visiting Hong Kong team took to the field for the final against the host nation on November 13. The incident enraged Hong Kong’s top officials and politicians, triggering a police investigation.

The video re-post came with a note allegedly added by the man, saying: “Thanks to Incheon, South Korea, for recognising Hong Kong’s national anthem,” according to the police source.

A force spokesman said the man was suspected of posting seditious messages on social media that provoked hatred among others towards the central people’s government and the city’s administration, and incited others to use violence, desecrate the national flag and insult the national anthem.

Some electronic communication devices police suspected had been used to publish the messages were seized in the searches, the spokesman said.

The man was detained for inquiries.