More clashes have broken out in Athens between Greek youths and police outside the country's parliament in Syntagma Square.
Costas Karamanlis, Greece's prime minister, who holds only a slim majority in parliament, dismissed opposition calls to quit, as Greece was hit by fresh anti-government protests on Friday.
Groups of students threw firebombs and rocks, while police fired back tear gas during an anti-government demonstration on Friday.
Several thousand people marched towards parliament chanting "blood demands vengeance" and "one underground, a thousand in the street".
Barnaby Phillips, Al Jazeera's correspondent in Athens, said that police had pushed the protesters from Syntagma Square to the nearby Ammonia Square and that the situation appeared "to have calmed down".
'Vengeance'
Phillips said: "They [the protesters in Syntagma Square] were pursued by riot police who were firing volley after volley of tear gas. The crowd were lobbing rocks and bricks and Molotov cocktails and trying to break their way into shop fronts.
"The police cleared them to the immediate vicinity of the square."
Phillips said many shopkeepers and businesses had begun criticising the government of its handling of the demonstrations.
He said: "The police are in a difficult situation. Ever since Grigoropoulos was shot... the last thing the police could risk was bloodshed or serious injuries among the protesters.
"So they seem to have more or less decided to let the protesters' fire burn out if you like."
The violence has shaken the weak conservative government of Costas Karamanlis, the prime minister, which was already under pressure over corruption scandals and unpopular reforms.
Greece's opposition has called for the government to resign.
High unemployment
Two more demonstrations were scheduled later on in the day in Thessaloniki, Greece's second-largest city.
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| Shopkeepers have criticised the police for their handling of the violence [AFP] |
Hundreds of cars, banks and businesses have been wrecked by rioting over the last week as young Greeks voiced their anger at high unemployment and low wages.
Criticising the government's slow response to the crisis, the Ta Nea newspaper ran the headline "The Bell Tolls For Karamanlis" across its front page on Friday.
The Ethnos newspaper ran the headline "Government Under Siege; Education Protests Escalate".
Many Greeks voiced anger that Epaminondas Korkoneas, the policeman charged with premeditated manslaughter, did not express remorse to investigators.
He said he had fired warning shots at Grigoropoulos and others in self-defence, with a ricocheted bullet ultimately killing the 15-year-old.
Korkoneas and another officer are being held in jail pending trial by a prosecutor.