BELGRADE, June 30, 2025 (BSS/AFP) - Serbian President Aleksandar Vucic insisted Sunday that he would not cave in to the 140,000 protesters who rallied in the capital overnight demanding early elections, while vowing more arrests following clashes.

Saturday's rally was one of the largest in more than half a year of demonstrations triggered by the roof collapse at a train station in the city of Novi Sad in November, killing 16 people -- a disaster widely blamed on entrenched corruption.

Unlike previous gatherings that had passed off without incident, this time police and protesters clashed after Saturday's demonstration.

"Serbia has won, and you cannot defeat Serbia by violence as some wanted," Vucic said in a speech.

Accusing the student-led movement of causing "terror", he promised more arrests over the violence.

AFP journalists saw riot police using tear gas and batons as protesters hurled flares and bottles at rows of officers in several clashes following the massive gathering in Belgrade.

Authorities said 48 officers had been injured, one seriously, and put the crowd size at 36,000 -- well below an independent estimate by the Archive of Public Gatherings of around 140,000.

Interior Minister Ivica Dacic said 22 people had sought medical help, of whom two were seriously injured.

- 'This is not the end' -

Police detained 77 people, and 38 were still in custody, Dacic added.

"There will be many more arrested for attacking police... this is not the end," Vucic said.

There would be "no negotiations with terrorists and those who wanted to destroy the state -- accountability follows".

"Revenge must not be our language, but responsibility must be part of our consciousness," said the president.

Later Sunday, eight people were arrested on accusations including planning to block roads and attack state institutions "in order to violently change the state order", the Higher Prosecutor's Office said in a statement.

After activists called for a protest in front of the prosecutor's office, at least 2,000 people gathered there Sunday evening, according to an AFP photographer.

"This is not a moment for withdrawal," the protest group said on Instagram ahead of the gathering.

In other parts of Belgrade, demonstrators blocked roads, including the major Autokomanda junction, where they set up tents, preparing for an overnight stay.

Similar blockades were also set up in several other Serbian cities, including Novi Sad.

- 'Take freedom' -

Ahead of Saturday's protest, organisers had issued an "ultimatum" for Vucic to call elections -- a demand he had dismissed well before the rally began.

On Sunday, he reiterated there would not be any national vote before the end of 2026.

The outcry over the Novi Sad disaster has already led to the resignation of the country's prime minister.

The governing party has stayed in power however, with a reshuffled administration and the president still in office.

Vucic has repeatedly alleged the protests are part of a foreign plot to destroy his government.

More than a dozen people have been arrested in recent weeks, a crackdown that has now become routine ahead of large demonstrations.

After the rally, organisers played a statement to the crowd calling for Serbians to "take freedom into your own hands" and giving them the "green light".

"The authorities had all the mechanisms and all the time to meet the demands and prevent an escalation," the organisers said in a statement on Instagram.