The stage was set for what could be the largest single protest since the anti-graft movement first coalesced after 15 people were killed when a railway station roof collapsed in the city of Novi Sad in November.

But with supporters of President Aleksandar Vucic’s embattled government also mobilising in the capital as well, there is growing concern about the risk of clashes.

Both the European Union and the United Nations on Friday appealed to the government to respect the right to demonstrate.

The railway station disaster ignited long-simmering bitterness over alleged corruption and lax oversight in construction projects.

For weeks, the student-led protesters have criss-crossed the country, holding rallies in Serbia’s major cities.

They have also taken their anti-corruption crusade to the rural villages and towns that have long been the backbone of support for Vucic’s government.

Their return to Belgrade on Saturday will likely further ramp up the pressure on the government, from which several high ranking officials, including the prime minister, have resigned in recent months.

– ‘I will not be pressured’ –

But supporters of the government were also mobilising in the capital, including ultranationalists, militia members, and alleged football hooligans who have set up barricades near the parliament.

That has led to fears of a confrontation with the student-led demonstrators planning to march by parliament on Saturday. On Friday evening, riot police fanned out near the encampment, which is surrounded with barricades and farming tractors. Vucic took to the airways with a defiant message as demonstrators began to trickle into the city, vowing to not back down in the face of mass protests.

“Just to be clear, I will not be pressured,” said Vucic during a national televised address. “I’m the president of Serbia and I won’t let the streets set the rules in this country.” He went on to call on all sides to refrain from using violence and instructed police to not use excessive force.

On Friday night, thousands lined Belgrade’s streets to welcome student protesters arriving in the capital after marching for days from cities across Serbia.

“There definitely won’t be any violence here because we all came with the same purpose — to wait for the people who marched, the people who are liberating Serbia,” said Tijana Djuric — a 20-year-old student at the Faculty of Economics in Belgrade.

– ‘Tensions’ –

Some analysts however warned that the situation could escalate. “We can already see for a few days that the regime is trying to escalate tensions,” said political analyst Srdjan Cvijic. “It is creating a Potemkin village of support in front of the presidency with pro-government demonstrators who are paid.”

Pressure has been mounting in the days leading up to Saturday’s rally. Government-backed media have broadcast increasingly inflammatory accusations, saying the students are planning to launch a “coup”.

Earlier, Vucic himself accused the demonstrators of organising “large-scale violence”. On Monday, police briefly scuffled with protesters who blocked the entrance to state broadcaster RTS in response to alleged unfavourable coverage of the demonstrations.

And last week, opposition lawmakers lit flares and discharged smoke canisters to show their support for the protests during the opening day of the spring parliamentary session. The government later said that several MPs were injured during the melee.

But even as Vucic warned of a “final” showdown on Saturday, student protesters said they would continue to rally until their demands for greater accountability were met. “If our demands are not met, we will remain in the streets, at blockades, in the fight – until justice is served!” read one post shared by a student group online.