Thousands of rioters across Greece have clashed with police in a third day of violent protests over the fatal shooting of a 15-year-old boy.
Police used teargas against protesters roaming the streets of Athens throwing petrol bombs and setting fire to buildings, vehicles and rubbish bins.
Dozens of people have been injured throughout the country and there are reports of looting in some areas.
Prime Minister Costas Karamanlis has gone on television to appeal for calm.
He said "extreme elements" were taking advantage of the situation to engage in vandalism and pledged to compensate businesses damaged.
The riots began on Saturday after Alexandros Grigoropoulos was shot dead by police in the Exarchia area of Athens.
Television pictures on Monday evening showed small fires burning in the centre of Athens and hundreds of people wandering through the streets, some attacking banks, businesses and vehicles.
A large Christmas tree in central Syntagma Square was set on fire and windows were smashed on hotels, government buildings and departments stores.
The BBC's Malcolm Brabant, in a hotel in the city surrounded by demonstrators, said he could see petrol bombs, flares and rocks being thrown towards parliament while protesters cheered.
There was a smell of tear gas and black smoke rising from the square, obscuring the famous Acropolis.
Joast Meijerink, a guest at an Athens hotel set on fire, told the BBC the rioters had caused significant damage to the capital.
"Everything that could be demolished was demolished," said Mr Meijerink.
Protests have also taken place at Greek embassies in Berlin and London, but there was no reported violence.
Earlier on Monday, hundreds of students clashed with riot police in Thessaloniki, Greece's second biggest city.
Students of the city's Aristotle university were reported to have stockpiled petrol bombs on campus, protected by laws preventing security forces from entering the grounds of schools, universities and polytechnics.
There was also trouble in the central city Trikala and police stations were attacked in Piraeus, Corfu and Thessaloniki, where an officer was injured.
Our correspondent says opposition parties are capitalising on the national sense of outrage and the government is getting the blame for an individual policeman's actions.
The government is extremely vulnerable, reeling from a series of scandals and only has a majority of one in parliament, he adds.
In a nationally televised address on Monday, Prime Minister Karamanlis called for calm, unity, restraint and a sense of solidarity with the dead boy's family.
"Unfortunately, extreme elements have exploited this sad event for their own purposes," he said.
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