THESSALONIKI— A police officer was arrested in northern Greece Monday after a 16-year-old boy was shot in the head and seriously injured during a car chase that began when he allegedly failed to pay the bill at a gas station. The boy, who has been hospitalized and is in critical condition, was not named but identified by relatives as being a member of the Roma minority.

The incident occurred outside Greece’s second largest city early Monday. Officers from a police motorcycle patrol chased the boy in a pick-up truck after authorities had been alerted by the gas station employee over the unpaid bill for 20 euros ($21).

The arrested officer was due to appear before a public prosecutor Tuesday to face charges of attempted manslaughter. The shooting occurred on the eve of annual protests in Greek cities to mark the fatal police shooting in 2008 of 15-year-old Alexandros Grigoropoulos in Athens, whose death triggered extensive riots that lasted for several weeks.

Anniversary protests held since the shooting have often led to violent clashes between protesters and riot police.

Asked to comment on the shooting, government spokesman Giannis Oikonomou said: “The value of a human life can never be measured by any amount of money.” Police said the officer, who was a passenger on one of the pursuing motorcycles, fired two shots to try and stop the suspect from ramming the bike.

A statement said the driver of the pick-up truck had “repeatedly made dangerous maneuvers” before the shots were fired, adding that the vehicle subsequently crashed. A spokesman for Greece’s main opposition, the left-wing Syriza party, accused the center-right government of failing to keep excessive policing methods in check.

“Society can no longer tolerate this climate of fear created by extreme police brutality which, for trivial reasons, has threatened the life of an underage 16-year-old child,” said Christos Spirtzis, the party spokesman for public order.