Officers identified them as a vice-chairperson of the group that organises the candlelight vigil, Chow Hang-tung, and a 20-year-old food courier.
“They were found to have used their social media accounts to advertise or publicise a public meeting that had been prohibited by the police,” said detective senior superintendent Terry Law.
But Law declined to reveal what exactly the pair had said on social media, calling their actions “extremely irresponsible” as people who had listened to their alleged appeals would have been in trouble too.
Asked why officers had decided to make the arrests on June 4, Law said they simply took action after gathering sufficient evidence and there were no other considerations.
Police banned the annual candlelight vigil at Victoria Park for a second year in a row, citing the dangers of allowing a public gathering amid the Covid-19 situation in the city.
The decision was upheld by an appeal board.
The Hong Kong Alliance in Support of Patriotic Democratic Movements of China, which has organised the candlelight vigil in previous years, had called on people to only commemorate the 32nd anniversary of the bloody crackdown in a lawful and safe manner.
Chow had earlier said she planned to go to Victoria Park in a personal capacity to light a candle for the victims.
Police sources have told RTHK that up to 7,000 officers will be deployed to handle potential June 4 gatherings, with around 3,000 officers sent to guard Victoria Park.
People who go near Victoria Park and are dressed in black, chant slogans, or light candles, the sources said, could be considered to be there in connection with the banned assembly.
Thousands of people defied last year’s ban on the Victoria Park vigil, but activists who took part, including Joshua Wong and Lester Shum, have been handed jail sentences.