The Serbian government has invited the FBI and Russia’s FSB to investigate allegations that authorities deployed a sonic weapon during a large protest in Belgrade on March 15.

The demonstration, which became the largest anti-government rally in Serbia’s history, was organised by students and marked the latest wave of opposition to President Aleksandar Vucic’s government.

Vucic, in a statement to the press, firmly denied that the government had used the controversial weapon against peaceful protesters. “We are not hiding anything, we are ready to officially invite the FBI and FSB to come to Serbia to verify all these allegations and facts,” he told reporters.

According to local authorities, the protest attracted around 100,000 participants, though independent estimates and aerial footage suggest the actual number could have been as high as 325,000.

The protest was remarkably peaceful, given its huge size and the expectation of violence in the days before. However, videos soon circulated on social media showing protesters scattering after a loud sound, with some speculating that it was caused by a sonic cannon.

As bne IntelliNews reported, the LRAC sonic cannon, an acoustic weapon capable of producing sound at a volume of up to 160 decibels, is designed to disorient or disperse crowds.

Opposition figures, including former Serbian president Boris Tadic, have called for an urgent investigation into the incident, with some requesting international oversight. Tadic suggested appealing for help from international bodies, including the United Nations, to probe the claims.

Serbia’s security services, including the Security Intelligence Agency (BIA), have rejected claims that the weapon was used. In a statement put out on March 17, the BIA stressed that no such device was deployed during the protest, and that no effects typically associated with a sonic cannon were observed by agency personnel. The agency also stated that it does not possess such a weapon.

In response to the controversy, Vucic maintained that the Serbian government had not employed any unusual crowd control methods, adding that Serbia’s armed forces do not possess such technology.

“We know that we didn’t use any sound cannon, the army doesn’t have one at all,” he said. The president also compared the situation to the 2014 Maidan protests in Ukraine, saying that false accusations were made against the government of Viktor Yanukovych to encourage regime collapse.

Serbia’s Interior Minister Ivica Dacic said the police had acted within the law during the protest and had made significant efforts to ensure the event remained peaceful. “The Serbian police did not use a sound cannon or any other illegal means,” Dacic said.

Despite the official stance, the allegations have prompted calls for independent scrutiny, with petitions circulating for a UN investigation into the potential use of the sonic cannon. Meanwhile, Serbian prosecutors and court staff are set to go on strike starting March 18, complicating the investigation process.

Vucic is expected to travel to Brussels on March 18 or 19 for talks with Nato Secretary General Mark Rutte and EU Enlargement Commissioner Marta Koss. In the coming weeks, he is also scheduled to meet with European Commission President Ursula von der Leyen.