Dimitri Messinis, Associated Press
A riot policeman's clothing catches fire after demonstrators threw gasoline bombs during a march to mark the first anniversary of the police shooting of a teenager in Athens.

ATHENS, Greece — Masked youths hurled firebombs and chunks of marble at police during a march in Athens on Sunday to mark the first anniversary of the police shooting of a teenager whose death sparked massive riots.

Police fired volleys of tear gas to disperse the youths in running street battles in the center of the capital as several thousand demonstrators commemorated the death of 15-year-old Alexandros Grigoropoulos. The teenager's death sent youths rampaging through cities for two weeks last December.

On Sunday, the rioters smashed bank windows, overturned trash bins and set them alight as they hurled rocks and fire crackers at riot police. Authorities said 177 people were detained for public order offenses in Athens and another 103 in the northern city of Thessaloniki, where a similar demonstration turned violent. Police also clashed with protesters in the southern city of Patras and the northwestern city of Ioannina.

At least five protesters and 16 police were injured in the violence, police said.

Police on motorcycles chased rioters amid scenes of chaos at Athens' main Syntagma Square, with youths punching and kicking officers pushed off their bikes. One policeman who lost control of his motorbike struck and injured a female pedestrian, who was tended to by demonstrators until an ambulance arrived to transport her to a hospital.

At Athens University, masked protesters broke into the building and pulled down a Greek flag, replacing it with a black-and-red anarchist banner.

Authorities said the university's dean was injured when the youths broke into the building, and he was hospitalized in an intensive care unit.

As night fell, about 200 masked demonstrators were holed up in the neoclassical university building, smashing marble chunks off the university steps and ripping up paving stones from the courtyard to use as missiles against the police, before eventually leaving the building.

Clashes between demonstrators and police continued late into the night at another campus building, the Athens Polytechnic, after about 400 people gathered at the site where Grigoropoulos was shot dead in central Athens' Exarchia district. Masked youths holed up in the building, which police are barred from entering, and emerged to hurl rocks and bottles at the officers, who responded with tear gas.

More than 6,000 police had been deployed across Athens in an effort to prevent violence.

The new Socialist government, which came to power in October and has been confronted with a surge in armed attacks by far-left and anarchist groups after last year's shooting, had vowed a zero-tolerance approach to violence.

Civil Protection Minister Michalis Chrisochoidis defended tougher tactics used by police, despite criticism from a left-wing opposition party which said the government's response had been heavy-handed.

"Police detentions, when justified, are not illegal in a democratic society. Neither is it illegal for judicial officials to press charges," the minister said.

"Vandals and hooligans have nothing to do with democracy."

In Thessaloniki, Greece's second-largest city, youths threw gasoline bombs at police, set fire to several cars and smashed 10 storefronts, including a Starbucks cafe.

In a newspaper interview published Sunday, Grigoropoulos' mother, Jina Tsalikian, described her son as a quiet and friendly boy who stayed away from demonstrations.

"Before his death, Alexandros was just a kid like all the others. But now he has become a symbol of the children of his generation," Tsalikian told the weekly Veto newspaper, challenging claims by a police officer charged with her son's murder that the boy had been hit by a warning shot.

"He was shot in cold blood — all the eye witnesses say this," she said.

Grigoropoulos was shot when two police officers on patrol confronted a group of youths in Exarchia, where protests frequently occur.

Two police officers have been charged with murder and attempted murder for the teenager's death. Their trial is to begin on Jan. 20.

Also Sunday, a soccer match at Athens Olympic stadium between local clubs Panathinaikos and Atromitos was suspended for 30 minutes because of tear gas used by police against rioters outside the ground.

Associated Press writers Demetris Nellas, Derek Gatopoulos and Karolina Tagaris in Athens, and Costas Kantouris in Thessaloniki contributed to this report.