Hong Kong police arrested on Friday pro-democracy politician Tam Tak-chi, who is expected to run for a seat in the legislature in September's election, on charges including incitement to participate in unlawful assembly.
Tam, 47, the vice-president of the People Power party and a former radio host, won an unofficial primary poll organised by the opposition to select candidates for the Legislative Council vote.
The arrest comes days after Beijing officials and Hong Kong leader Carrie Lam said the primaries were illegal and may violate a new national security law.
After hearing the charges, Tam told reporters they were unrelated to the new law.
Police said the incitement to take part in an unlawful assembly charge was related to a January protest. It did not say what the charges for seditious intention and disorder in public places were related to.
Tam said they were for swearing at the police and shouting "Liberate Hong Kong! Revolution of our times," in January, a slogan the government declared illegal earlier this month under the new law, which is not retroactive. Sedition is covered by British colonial era legislation.
When addressing reporters, Tam shouted the slogan again.
The Beijing-drafted law introduced last month punishes what China broadly defines as subversion, secession, terrorism and collusion with foreign forces with up to life in prison.
Critics of the law fear it will crush the wide-ranging freedoms promised to the territory when it returned to Chinese rule in 1997. Supporters say it will bring stability after last year's often-violent anti-government and anti-China unrest.
Soon after Beijing said the weekend primaries vote was illegal, former Hong Kong lawmaker Au Nok-hin said he was pulling out as an organiser of the poll due to the accusations.
On Thursday, another organiser, Andrew Chiu of the Democratic Party, said his work was done and he would no longer help coordinate the Legislative Council election campaign.
Veteran democrat Benny Tai, who was singled out in Beijing statements about the vote, also posted on Facebook there was "not much left to do" and he would now focus on academic work.
A younger, more defiant generation, including prominent activist Joshua Wong, overshadowed the old-school Hong Kong democrats in the primaries.
The registration for candidates in the September elections begins on Saturday.
Wong was disqualified from running in lower-level district council elections last year, where the democrats nevertheless won more than 80% of the seats.