Tens of thousands of Serbians returned to the streets Saturday to honor the victims of the roof collapse at Novi Sad’s train station last year, which killed 16 people and triggered nationwide protests marked by police violence and calls for the government’s resignation.

A 16-minute silent vigil at the train station was held at 11:52 a.m, the time of the collapse, to honor each of the victims. A mass demonstration will also follow Saturday’s tribute, as thousands of people across Serbia have come to Novi Sad to join the commemoration.

Serbia’s government has declared Saturday a national day of mourning. But President Aleksandar Vučić has threatened to arrest mourners if they “resorted to violence.”

Vučić downplayed Saturday’s events when asked by reporters. “What is happening in Novi Sad? Is some soccer match being played?” he said.

Authorities also canceled all rail transport in the country on Friday, claiming a bomb threat; however, media reports suggest it was a move to prevent citizens from reaching the city for the demonstrations.

What began as a demand for accountability over a tragedy blamed on government negligence quickly escalated into nationwide protests over the past year. Widespread police brutality fueled the unrest, eventually prompting President Aleksandar Vučić to try to calm the outrage by forcing Prime Minister Miloš Vučević to resign along with the rest of his cabinet.

Serbia became an EU candidate country in 2012, and it later opened accession negotiations with the EU in 2013. European Commission President Ursula von der Leyen recently urged Vučić and Serbia to “get concrete” about joining.