Serbian officials have denied that the country's security forces used a military-grade sonic device to disperse and scare peaceful protesters at a major anti-government rally over the weekend.
Opposition officials and Serbian rights groups claimed that the widely banned acoustic weapon, which emits a targeted beam to temporarily incapacitate people, was used.
They say they would file charges with the European Court of Human Rights and domestic courts as confusion continues to swirl over the incident.
Protesters gathered from all over the country as the government struggles to stem the months-long outrage over the deadly fall of the Novi Sad railway station canopy in November.
Between 275,000 and 325,000 people took part in the protest, according to the Public Assembly Archive, an organisation that monitors crowd size.
That figure is higher than the 107,000 estimated by the government.
Earlier this week, Serbia's populist President Aleksandar Vucic warned that security would use force against people at the rally.
He also said the demonstrators would never force him to stand down.
"You will have to kill me if you want to replace me," he said.
Footage shows crowd part down the middle
Footage from the rally shows people standing during 15 minutes of silence for the rail station disaster as they suddenly part down the middle and rush off the street.
Speaking with German broadcaster Deutsche Welle, protester Dušan Simin said the noise sounded like a "plane was landing from the direction of the presidency building".
"We couldn't run away from it, we didn't know what to do," he said.
"People must have instinctively thought something was coming down the street, so they started running to the side and we all fell over each other."
The Belgrade Centre for Security Policy, a non-government organisation, condemned what it called "the unlawful and inhumane deployment of prohibited weapons, such as acoustic devices, against peaceful protesters".
"The use of acoustic devices and similar weapons is illegal, as they are not listed among permitted crowd-control measures under the current Police Law."
Balkan news broadcaster N1 quoted military analyst Aleksandar Radic, who suggested a sonic cannon, or long range acoustic device (LRAD), caused the unexpected noise.
"In a situation when all the demonstrators were peaceful, when a 15-minute message was being given to victims, the weapon was used," Radic alleged on N1.
"The only goal of that act is a brutal display of force, proof of arrogance, and the motive is hatred towards one's own people."
James Parker, an associate professor at Melbourne University who is the director of a research program titled "Law, Sound and the International", said LRADs were sometimes referred to as sonic weapons because of their so-called alert tone.
He said in this instance the alert tone did not appear to have been used, but stressed there was not enough information to make a firm judgement about what happened.
"[The tone] sounds kind of like a siren and is deliberately in the mid to high frequency range, which is where the human ear is most vulnerable to discomfort, pain and in some cases, permanent damage," Dr Parker tells the ABC.
"In the video, it's not clear whether those frequencies are necessarily likely to cause hearing damage.
"But what's really obvious is that people are terrified, which is a bit different to usual LRAD videos."
Dr Parker says in typical LRAD videos, people normally grab their ears and slowly start to run away, because even if it's painful they're familiar with a siren noise.
But this doesn't seem to happen.
"I think that video looks like people freaking out and don't understand if it's a sound or some kind of thing coming towards them.
"The video looks like sound is being used to produce fear.
"That's my initial reaction but there's no way of me telling whether they're using an LRAD."
He said LRADs could be attached to an MP3 player and that sound could be produced that way, but he was unsure whether it would create the whooshing effect reported by protesters.
Serbian officials deny use of weapon
Serbian police and the defence ministry denied that an LRAD was used.
The Serbian president on Sunday urged judicial authorities to respond to the information "that sonic cannons were used during the protests," the state RTS broadcaster reported.
"I am asking … the ministry of justice and the prosecutor's office to react, either to prosecute those who used it, and we know they didn't but let's check," Vucic said.
"Let there be a proceeding but then they should also prosecute those who went public with such a notorious lie."
Belgrade's hospital has denied reports that many people sought medical help after the incident.
Does Serbia own a sonic acoustic weapon?
Serbia has not denied that it has the acoustic device in its arsenal.
In 2022, the Ministry of Internal Affairs attempted to legalise acoustic devices as crowd-control tools, the Belgrade Centre for Security Policy said.
But following public pressure, the draft was withdrawn.
However, it's believed a new draft law is currently under development, though it remains closed to the public.
What are the symptoms of a sonic weapon?
Sonic or ultrasonic weapons are devices that use sound waves to injure or incapacitate an opponent.
According to experts, those exposed to the weapon can experience:
- Sharp ear pain
- Disorientation and panic
- High blood pressure
- Nausea
Prolonged exposure can cause eardrum ruptures and irreversible hearing damage.
Why are people in Serbia protesting?
Authorities have faced near-daily protests since last November when a station roof collapsed killing 15 people in Novi Sad, Serbia's second city.
Students, teachers and other workers blamed rampant government corruption and negligence for the disaster.
They are also demanding release of documents about the disaster and accountability for those responsible.
The protesters believe the disaster reflects more than a decade of governing by Vucic — who closely associated himself with the station's recent renovation.
Despite multiple resignations, including then prime minister Miloš Vucevic, and Vucic's insistence that he is going nowhere, the protests have grown over the past four months.
"Today we will demonstrate our dissent … to show what we are striving for, a normal state, a state of law, without corruption, lying, media pressures, persecutions," said Aleksa Cvetanovic, a 23 year-old student.
Prosecutors have indicted at least 16 people, including former construction minister Goran Vesic, for the rail disaster.
But the charges have yet to go to trial.
ABC/wires
