BELGRADE, Serbia (AP) — Tens of thousands of anti-government protesters on Saturday staged marches in Belgrade and other Serbian cities against President Aleksandar Vucic, pledging to “radicalize” weeks of peaceful gatherings that have already shaken his populist rule.

The demonstrators in Belgrade blocked the main highway that leads through the capital and chanted slogans for Vucic to resign, something that he has repeatedly rejected over the past seven weeks of protests.

The protest initially erupted in response to two back-to-back mass shootings in early May that left 18 people dead and 20 others wounded, many of them pupils from a Belgrade elementary school.

The protesters have been demanding the resignations of top Serbian security officials and the revoking of broadcasting licenses for pro-government media and tabloids that regularly air violent content and host crime figures and war criminals.

The protesters consider that the state-controlled media is responsible for the culture of violence that has been mainstay in Serbia since the wars in the Balkans in the 1990s that left more than 100,000 people dead.

Vucic, a former ultranationalist who took an active role in the breakup of the former Yugoslavia, now claims he wants to take Serbia into the European Union. He has said he will never accept the opposition demands. He has branded protest leaders as “hyenas" who want him and his family dead.

One of the protest leaders, Aleksandar Jovanovic, said that the demonstrations will continue, and vowed to further “radicalize” them with the blockade of roads and government buildings throughout Serbia.

“Serbia will stop," he said. “We have to clean out this poison.”