The movie Bullet's Flight by director Beata Bubenets was due to be screened at the documentary film festival Artdocfest in the Oktyabr movie theater on December 10, RFE/RL said.

Read alsoRFE/RL: Moscow theater director ordered under house arrest in Serebrennikov caseBut reports said several individuals sprayed an acrid liquid in the hall, prompting an evacuation.

The leader of the South East Radical Block (SERB) movement, Igor Beketov, was reportedly among three members of the group detained by police over the incident.

Law enforcement authorities have not commented.

The war in Donbas, eastern Ukraine, has killed more than 10,000 people since April 2014.