Students at the University of Novi Sad said on September 14 that independent laboratory tests showed police had used a banned form of tear gas against demonstrators during clashes earlier this month, and demanded an investigation into those responsible.

The Faculty of Sciences (PMF) students said that analyses confirmed the presence of CS gas and CN gas, or chloroacetophenone, which was widely phased out in the 1970s due to its high toxicity. CN was banned by the United Nations in 1969.

“Due to its high toxicity and serious health consequences, CN gas was completely replaced by CS gas in the 1970s … the use of CN gas is not a means of control, but the poisoning of citizens,” the students said in a statement posted on social media. They urged criminal accountability for those who authorised its use and said they were ready to provide collected samples for further testing.

Thousands of people rallied in Serbia’s northern city of Novi Sad on September 5 against police violence and what they described as violations of university autonomy. Clashes broke out after police tried to disperse the demonstrators, who had earlier been evicted from occupied faculty buildings. 

According to the students, dozens of discarded canisters were collected after the protest, some with markings removed. They said the tests were conducted using gas chromatography with mass spectrometry, the same method employed in accredited laboratories worldwide.

The interior ministry in Belgrade rejected the claims. “The Ministry of the Interior categorically denies the allegations … the police do not possess such a thing and therefore cannot use it,” it said in a statement.

Serbia has been rocked by protests for the past ten months, mostly peaceful until mid-August, when demonstrators clashed with police and set fire to ruling party offices.