Riot police fought running battles with hundreds of protesters outside Greece's parliament today while the opposition socialist party called for elections to end four days of protests.
Rows of riot police squared off with demonstrators for more than an hour outside parliament before firing teargas to disperse the crowd.
Bands of young protesters regrouped to throw stones at police and chanted: "Let parliament burn!"
Violence spread to the Athens suburbs after the funeral of a 15-year-old boy, Alexandros Grigoropolos, whose shooting by police on Saturday triggered Greece's worst riots in decades, fanned by discontent at government scandals and a slowing economy.
More than 5,000 people dressed in black gathered at the cemetery, many chanting: "Cops, Pigs, Murderers".
As the boy's flower-covered white coffin was being buried, protesters clashed with police outside and one officer fired shots in the air to disperse an angry crowd.
His killing touched a raw nerve among young Greeks, outraged at years of political scandals and rising levels of poverty and unemployment, worsened by the global economic downturn.
Prime Minister Costas Karamanlis, whose party has a one seat majority, held emergency talks with the president and opposition leaders to urge them to close ranks against the rioters.
"We must all have a united stand against illegal actions, to clearly condemn violence, looting and vandalism," he said, and appealed to unions to cancel a protest rally during a 24-hour strike scheduled for tomorrow.
Police fear the strike, expected to ground flights and bring Greece to a standstill, will fuel more violence.
Both requests were quickly rejected by leftist union leaders and politicians who say the government's reforms have worsened conditions for the one-fifth of Greeks below the poverty line.
Protests have swept more than 10 cities across the European Union member state of 11 million people, including the tourist islands of Crete and Corfu.
Hundreds of buildings have been wrecked or burned and more than 50 people injured. Police decline to give damage figures, but conservative estimates put it at millions of euros.
More than 130 shops have been destroyed in the capital, dashing retailers' hopes that Christmas would compensate for Greece's darkening economic outlook.
One policeman has been charged with murder over Grigoropoulos' shooting. Police said the officer fired three warning shots after their car was attacked by 30 youths on Saturday but witnesses said he took aim.
Police have arrested some 200 people, some for looting, during the protests but have tried to avoid direct fighting which might worsen tensions, police officials say.
Greece has a tradition of violence at student rallies and fire bomb attacks by anarchist groups, which have heightened tensions with police.