THESSALONIKI, Greece (AP) — Anarchists have clashed with riot police in Greece after some 2,000 protesters from across the Balkans marched in the northern Greek city of Thessaloniki against nationalism in the region.

Police used tear gas and threw stun grenades Saturday at the anarchists, who were barricaded inside the University of Thessaloniki campus. Police are prohibited by law to enter the campus to make arrests.

The gathering of Balkan anarchists was organized after far-right activists burned down an anarchist collective’s premises in Thessaloniki in January.

Nationalist tensions remain pervasive in the Balkans, and Greece and neighboring Macedonia have seen recent protests over a decades-long name dispute. Greece argues that Macedonia’s name in its current form implies a territorial claim against its own region with the same name.