Hundreds of masked protesters hurled petrol bombs and clashed with police outside parliament in Greece as lawmakers debated more austerity measures on Tuesday.
The trouble began when youths, mainly students, marched in central Athens to mark the police shooting of a student in 2008.
Police fired teargas at the protesters who pelted them with broken pavement slabs, sticks and petrol bombs for nearly an hour.
A second bout of trouble broke out when thousands joined an evening march, prompting police use tear gas again, and form a cordon outside parliament.
Fifteen people are reported to have been detained.
The 2012 budget was passed by Parliament on Wednesday. It contains tax rises and spending cuts aimed at cutting the deficit and showing foreign lenders that Greece is back on track to sorting out its finances.
The budget is designed to cut the deficit to 5.4% of gross domestic product from a projected 9% this year.
It was submitted by an interim coalition government led by former bank governor Lucas Papademos, who took office on 11 November.
