BELGRADE, Serbia — As tensions in Serbia soar, students and other opponents of the populist president are gearing up for a major rally in the capital, Belgrade, over the weekend.

Momentum has been building in favor of their demands for major changes in the Balkan country, after nearly four months of student-led anti-government protests.

Some believe that the demonstration on Saturday could mark the “D-Day” and endgame that have shaken the firm grip on power of authoritarian Serbian President Aleksandar Vucic.

As thousands of protesters arrive in Belgrade from all over the country, Vucic has warned that the rally could end in bloodshed. He threatened mass arrests of the protesters if they turn to violence, and said the only way he would leave power was “if they kill me.”

Most of the student led-protests have so far been peaceful, with sporadic incidents caused by Vucic supporters. But this time, the president’s loyalists started arriving in the capital from all over the country days ahead of the scheduled opposition rally. They set up a tent camp in a park in front of the presidential palace downtown, creating a de facto human shield for Vucic.

The crowd, which had grown to a few thousand by Thursday lunchtime, included some pro-Vucic students who claimed they “just want to resume learning” after most universities shut their classes following the protests.

However, the occupants of the camp include veterans of a dreaded paramilitary unit that committed war crimes during the wars in the Balkans in the 1990s. Well-known figures from Serbia’s flourishing criminal underworld could also be seen, along with soccer hooligans who routinely resort to violence and have been supporting Vucic, acting as guards at some of his rallies.

The catalyst for monthslong protests was the deadly collapse of a railway station canopy in the northern city of Novi Sad on Nov. 1 which resulted in 15 fatalities. This incident has been widely attributed to governmental negligence, endemic corruption and shady deals made with Chinese construction companies that took part in the recent renovation of the station.

Initially, the protests began as sporadic demonstrations seeking accountability for the Novi Sad tragedy. However, they rapidly evolved into a nationwide movement addressing broader issues such as demands for major democratic reforms.

The movement has garnered extensive support from various segments of Serbian society.

Vucic has tried to ease the pressure by sacrificing the prime minister, who resigned in December along with the government. He put forward draft legislation on university education, while 16 people were charged over the disaster in Novi Sad.

At the same time he has described the protests as a ploy organized in the West to oust him from power. Vucic sought and obtained support from Russia’s President Vladimir Putin while cracking down on liberal rights groups at home.

The rally is open-ended and may continue after Saturday, and student organizers say there may be further protests to come.

“We are not taking the final steps — we are making tectonic changes. If our demands are not met, we will remain on the streets, in blockades, in the fight until justice is served,” they said on Instagram.

Similar student-led rallies already have been held in Novi Sad, the central city of Kragujevac and Nis, in the country’s south, drawing tens of thousands of people and lasting for a day or longer.

Thousands of people from all over Serbia are expected to converge on Belgrade by Saturday. Already, hundreds of students have begun marching on the capital from various directions, while some are also cycling.

The citizens of Belgrade, a city of some two million people, also are likely to swarm the streets in huge numbers as support for the student-led protests has persisted despite Vucic’s campaign against them.

The gathering on Saturday could easily turn into the biggest rally ever in the troubled Balkan nation, which has a long history of anti-government demonstrations.

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Associated Press writer Jovana Gec contributed.