Riots broke out Sunday in the Greek capital and the northern city of Thessaloniki as demonstrators protested the fatal police shooting of a teenager in Athens the previous night.

Youths hurled firebombs, rocks and other objects at riot police, who responded with tear gas.

The circumstances surrounding the shooting of a 16-year-old boy by a police special guard in the downtown Athens district of Exarchia are still unclear. But the death triggered extensive riots in cities around the country overnight, with youths burning shops, setting up flaming barricades across streets and torching cars.

More riots broke out during demonstrations on Sunday, with protesters in Greece's second largest city of Thessaloniki attacking City Hall, two police precincts, several shops and a bank. They also attacked vans and cars belonging to several Greek television channels.

The march of about 1,200 people turned violent when participants began pelting the police precinct, already targeted on Saturday night, with rocks and firebombs. Others erected barricades on central roads using blazing trash bins.

Shops were smashed and a firebomb damaged a bank branch, the third such attack in Thessaloniki since Saturday night.

In Athens, more than two thousand protesters began marching to the capital's police headquarters. Violence quickly broke out, with demonstrators throwing rocks and firebombs, damaging several shops and banks.

Firebombs also damaged an office building belonging to the Environment and Public Works Ministry. Police were using large amounts of tear gas to contain the rampaging youths.

Earlier, Interior Minister Prokopis Pavlopoulos had called for restraint during the demonstrations. He expressed the government's deep sadness over the teenager's death, and both he and Deputy Minister Panagiotis Chinofotis submitted their resignations, which were not accepted by the prime minister.

Police said that the two officers involved in the shooting claimed they were attacked by a group of youths in the Exarchia district. One responded by throwing a stun grenade, and the other by firing three shots. At least one shot hit the teen in the chest.

Exarchia, home to music clubs, bars and increasing number of upscale restaurants, has long been considered a haven for anarchists and drug users. Clashes often break out during demonstrations in Greece, and anarchists frequently firebomb banks, car dealerships and vehicles with diplomatic license plates.

After the shooting, hundreds of youths in Athens, Thessaloniki, Chania in Crete and other Greek cities hurled firebombs, rocks and other projectiles at police, who responded with tear gas. Rioters set up burning barricades across city streets, lit fires and smashed storefronts and bank branches.

On Sunday, crews cleaned up streets littered with the debris of smashed and burned businesses and banks and the charred remains of cars, while tear gas still hung in the air.

Twenty-four police were hurt in overnight rioting, and one remained hospitalized Sunday morning, Athens police said. It said rioters damaged or burned 31 stores, nine bank branches and 25 cars, including six police cars. Six people were arrested, five of them for theft from damaged stores and one for carrying a weapon, it said.

The two officers involved in the shooting have been suspended pending the outcome of the investigation, as has the police chief in the Exarchia precinct.

Pavlopoulos promised there would be a thorough investigation into the teenager's death and pledged to punish anyone found responsible.

"It is inconceivable for there not to be punishment when a person loses their life, particularly when it is a child," Pavlopoulos said during a news conference Sunday morning. "The taking of life is something that is not excusable in a democracy."