'Unfair but necessary'
Once news that the vote had passed trickled out to the streets of Athens, fighting broke out with a new level of brutality, says the BBC's Malcolm Brabant in the Greek capital.
The riot police engaged in behaviour that would never be tolerated in other parts of Europe, throwing stones back at the protesters, says our correspondent.
Police corralled demonstrators into the metro station outside parliament in Syntagma Square, and fired tear gas down the stairwells, he adds.
Meanwhile, protesters set fire to a post office on the ground floor of the finance ministry in the square.
The air outside parliament was thick with plumes of tear gas and smoke as clashes continued near the square between masked protesters - armed with rocks and sticks - and riot police firing tear gas and stun grenades.
Dozens of police and protesters were injured in the violence.
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