More than 1,000 protesters gathered in Bangkok for a pro-democracy rally on Wednesday, with tensions high in Thailand after the arrest of 21 pro-reform activists a day earlier.

The activists are part of a movement that has organised rallies since July, calling for an overhaul of the government and the resignation of Prime Minister Prayuth Chan-ocha. Some have also demanded reforms to the unassailable monarchy.

The gathering comes a day after protesters, staging an impromptu rally at the same site, clashed with police. Police arrested 21 activists who were “uncooperative” as officials tried to empty the area for King Maha Vajiralongkorn’s motorcade.

Protesters raised a three-finger salute as the motorcade drove by on Tuesday, a gesture the pro-democracy movement has borrowed from the popular Hunger Games films.

The youth-led pro-democracy movement is the latest in Thailand’s modern history, which has seen a cycle of opposing political factions taking to the streets in violent protests followed by coups from a putsch-happy army.

Wednesday’s demonstration was intended to commemorate the 47th anniversary of the October 14, 1973, student uprising against a hated military dictatorship during which 77 people were killed.