A Serbian rights group said Wednesday its activists were beaten after interrupting an event organized by the ruling populists that included an appearance by a convicted war criminal.

Youth Initiative for Human Rights said its nine activists were hurt, two of whom sought medical help after the incident late Tuesday in Beska, northern Serbia.

The group said they broke into the event hosting Veselin Sljivancanin, a former Yugoslav army officer sentenced by the U.N. court in the Netherlands for war crimes during Croatia's 1991-95 war.

Activists spread a banner reading "War criminals must shut up so we can talk about victims," but were thrown out and allegedly beaten outside the venue.

One activist, Ana Mitic, told local N1 television that "several men followed us through the corridor and then continued to beat us."

"They beat us hard and we started to run," Mitic said, claiming that the attackers kicked one of the activists who fell down on the floor.

The governing Serbian Progressive Party has protested an intrusion by "hooligans" and the "fascist incident." The party urged the authorities to punish those responsible.

Serbia has seen a resurgence of nationalism stemming from the 1990s Balkan war in which some 100,000 people died. President Tomislav Nikolic last week met with another convicted war criminal, former Bosnian Serb leader Momcilo Krajisnik.

The youth group criticized a "warmongering tone" by Serbia's government and ruling party officials as "very dangerous" and a threat to peace and stability in the Balkans.