Athens, Greece (CNN) -- The anniversary of a fatal police shooting triggered a new riot in Greece's capital Sunday, with protesters occupying a university building and throwing rocks and burning garbage at police.
Riot police with gas masks and shields faced off against about 200 demonstrators, some of whom attacked and injured the dean of the University of Athens following a protest march Sunday afternoon, authorities said. The protesters were holed up inside and around the school's administration building.
Police are barred from entering the downtown campus. Demonstrators broke up masonry from the courtyard of the 19th-century building and hurled chunks of the stone at police, who responded with stun grenades and tear gas and imposed a blockade of the building.
The university's dean, Christos Kittas, was in intensive care after being attacked, and 16 police officers were injured, Greek authorities said.
At one point, both sides halted their confrontation to let an elderly man on a motor scooter pass between their lines -- only to resume the melee once he was gone.
Skirmishes between police and demonstrators continued past nightfall, but some of the demonstrators were dispersing.
Protests began Saturday night to commemorate the December 2008 killing of 15-year-old Alexandros Grigoropoulos, whose death at the hands of police sparked rioting at the time by young self-styled anarchists across Greece. Police said they had made more than 230 arrests since the demonstrations began.
Sunday's protest march drew several thousand people and was generally peaceful, but a few hundred -- including some children -- broke off from the march to occupy the university campus.
Authorities have been barred from entering university grounds without the consent of the students since tanks crushed a 1973 student uprising protesting the military junta that then ruled Greece.
John Psaropoulos contributed to this report for CNN.