Greece's coalition government on Wednesday passed an austerity 2012 budget aimed at shrinking its debt mountain with tax hikes and spending cuts, hours after protesters clashed with police outside parliament.

Three major parties backing technocrat Prime Minister Lucas Papademos solidly voted for the budget, a package of deeply unpopular measures needed to cut the deficit and show foreign lenders the country is sorting out its finances.

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"Successful implementation of this budget will restore the country's international credibility and create the conditions to rescue the economy," Papademos told lawmakers. "We can't afford to keep whining...the targets are ambitious but feasible."

But one of the leaders, conservative party leader Antonis Samaras, made clear his support was solely aimed at rescuing Greece from immediate default and vowed to soften tax steps and boost growth measures if he wins power in elections expected in February.

"Our disagreements remain... we are approving the budget because it is an absolute priority to safeguard the viability of Greek debt," said Samaras, whose New Democracy party is the front-runner to win the next election but fall short of an absolute majority.

Samaras, who has long opposed the EU/IMF austerity policies imposed by his Socialist rival, former prime minister George Papandreou, under a 110-billion euro bailout agreed in 2010, made clear he will insist on snap elections in February, after Athens clinches a bond swap deal to cut the country's debt.

As lawmakers debated the budget, hundreds of masked youths hurled petrol bombs and clashed with Greek police outside parliament. See the story here.

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Firebombs, stones and bottles were thrown Tuesday as several hundred anarchists clashed with riot police outside the Greek parliament, where lawmakers were debating the 2012 budget before a vote expected after midnight.

The rioters were part of a march to commemorate the third anniversary of the fatal police shooting of a teenager in central Athens, according to The Associated Press.

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After anarchists threw stones, bottles and firebombs at the police, the officers responded with tear gas and stun grenades.

Police formed a cordon outside parliament, Reuters reported, and the rioters later moved away from parliament.

In a separate march earlier Tuesday, about 2,0000 students commemorating the teen's shooting hurled rocks and bottles during at police, as well as smashing two nearby store fronts and three bus stops. Other groups of teenagers attacked two suburban police stations with rocks and bottles.

Police dispersed the youths with a small amount of tear gas after the protesters used at least two fire bombs.

Police reported 14 officers were injured; nine people were arrested and six detained.

The shooting death of 15-year-old Alexis Grigoropoulos on Dec. 6, 2008 sparked two weeks of the worst rioting the country had seen in decades.

Some 5,000 police were on duty in the capital for Tuesday's rallies.

Violence was also reported in Greece's second-largest city, Thessaloniki, where police detained two people after a crowd of youths threw rocks at a government building.

There were also violent clashes in at least six other cities. In the city of Agrinio in western Greece, a group of students broke into the city hall while the city council was in session and ransacked some offices, throwing office supplies out the windows.

Last year, a court sentenced a police officer to life in prison for Grigoropoulos' death, and a second officer to 10 years.

The Associated Press and Reuters contributed to this report.