ATHENS, Greece (AP) — A Greek riot police officer who was shot with a flare during fan violence in Athens three weeks ago has died in a hospital of his injuries, health authorities said Wednesday.

On Dec. 7, a group of fans left a volleyball match to attack riot police stationed outside the arena with flares and gasoline bombs. Organized soccer fan groups are believed to have been involved. Police officer Giorgos Lyggeridis, 31, was shot in the thigh, suffering severe arterial damage. The clash prompted a government crackdown on sports violence.

An 18-year-old man has been arrested and charged with firing the flare.

Greece’s minister for the police, Giannis Economou, expressed his condolences to the police officer’s family and called for a “steadfast social alliance against violence.” He pledged that police efforts would continue “until we identify those who organized, coordinated and armed” participants in the Dec. 7 attack.

The center-right government has ordered all top-flight Greek soccer matches to be played without spectators for two months. Clubs must install surveillance cameras inside stadiums and organize personalized ticketing systems before fans are allowed back.

Violence has plagued Greek soccer for decades, despite repeated efforts to crack down on the supporters’ associations blamed for attacks, which mostly occur outside stadiums.