The protest marked the one-month anniversary of the country's first school shooting on May 3, when a teenager killed ten in an elementary school. In the second shooting on May 4, a 21-year-old man killed eight in a town outside Belgrade.

In response to the shootings, the government announced school summer holidays would start on June 6, two weeks earlier than planned.

Opposition parties which organised the protest - the fifth in the space of a month - say the government of President Aleksandra Vucic has failed to tackle the promotion of violence in the media and allowed it to permeate society.

Recent Serbian reality TV shows have featured convicted criminals, including murderers, and shown men beating up women.

Protesters on Saturday shouted "Vucic leave," and held up banners with the slogan "Serbia against violence".

Nenad Hadzi Maricic, an actor who was the main speaker at the event, voiced the protesters' demands which include the dismissal of Interior Minister Bratislav Gasic and Secret Service Chief Aleksandar Vulin as well as the immediate halt of all TV programmes that promote violence.

Vucic denies the allegations and says the government needs to be challenged in an election. Pink TV has pledged to stop airing a reality show which features a man convicted of murder from next week.

"We must remain persistent in our demands," Aleksandar Saran, one of the protesters told Reuters. "Our demands are not abstract, we just want to live in a healthy environment."

(Reporting by Ivana Sekularac; Editing by Christina Fincher)