A rally in the Greek capital turned violent when protesters in Syntagma Square lobbed Molotov cocktails at police, who retaliated by firing tear gas at the demonstrators.

Security forces also reportedly used flashbang grenades and pepper spray to push protesters back from the parliament building. According to Greek newspaper Kathimerin, the police had been ordered to refrain from using chemicals against protesters.

Around 70,000 people, as estimated by Reuters, gathered in front of the parliament for the country's biggest anti-austerity protest since the new government came to power.

"EU, IMF out!" shouted the angry crowd.

"For the past two-to-three years we've been living an incredible social catastrophe," one of the protesters told Agence France Presse. "My salary has been cut by 50 percent. I have two children and tomorrow I don't know if I'll have a job."

Clashes erupted in different parts of Athens Syntagma Square, with demonstrators throwing fire bombs at police.

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© Reuters / Yorgos KarahalisA riot police officer prepares to throw a teargas cannister to protestors during clashes near Syntagma square during a 24-hour labour strike in Athens.

Witnesses reported smoke rising over the square as security forces dispersed most of the protesters. Some remained, and continued the demonstration; others relocated to the streets of Panepistimiou and Benaki, where again started clashing with riot police.

Some 120 arrest were made throughout the capital. Police say protesters smashed bus stop kiosks and set fire to garbage cans.

Several people sustained injuries.

More than 3,000 police officers - double the usual number - were deployed in the capital of Athens to counter the protesters.

On Wednesday, Greece was gripped by a 24-hour general strike, which halted transit and other industries nationwide. Flights and trains were suspended, shops were shuttered and the hospitals were forced to rely on emergency staffing. The strike was called by the country's two largest trade unions, representing half of Greece's workers.

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© Reuters / Yannis BehrakisTeargas canisters explode beside riot police officers near Syntagma square during a 24-hour labour strike in Athens.
As many as 350,000 Greeks poured out into streets across the country to protest austerity, estimates the civil servants union ADEDY.

In the second largest city of Thessaloniki, around 18,000 demonstrators rallied. Greeks wrote on Twitter that large numbers of protesters are rallying peacefully in the streets. Earlier demonstrations there saw youths setting fire to debris, burning an EU flag, and then clashing with riot police.

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© Reuters / Yannis BehrakisSupporters of the Greek Communist party march by the parliament during a 24-hour labour strike in Athens.
Greece recently enacted a new round of spending cuts, totaling โ‚ฌ11.5 billion ($15 billion). The austerity measures are a precondition for another rescue loan from the European Central Bank; without the bailout, Greece could face bankruptcy in a matter of weeks.

"The new measures are unbearable, unfair and only worsen the crisis. We are determined to fight until we win," Costas Tsikrikas, head of the ADEDY public sector union told Reuters. "We call on all workers to join us in the march against the policies that the troika is imposing."

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© Reuters / Yannis BehrakisA demonstrator throws a molotov cocktail to riot police officers near Syntagma square during a 24-hour labour strike in Athens.
Greece is currently grappling with record unemployment levels, with over 30 percent of the country living below the poverty line.

The Greek government is planning to reduce pensions and increase the retirement age to 67 to cope with the country's budget crisis.

Two weeks ago, anger over Greece's new austerity measures spilled into the streets, with thousands protesting the drastic proposed budget cuts.

Last February, the country witnessed days of violent clashes in several cities, with police using tear gas and protesters throwing petrol bombs and stones.

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© Reuters / Yannis BehrakisA riot policeman is engulfed by flames after a protester threw petrol bombs in Athens' Syntagma square during a 24-hour labour strike.

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© Image from Twitter.comPhoto by user jamesmatesitv shows petrol bombs hitting ranks of riot police during an anti-austerity rally at Syntagma Square in Athens on September 26, 2012

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© Reuters / Yorgos KarahalisA riot police officer throws a teargas cannister to protestors during clashes near Syntagma square during a 24-hour labour strike in Athens.

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© APScreenshot from AP video.

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© Reuters / Yorgos KarahalisA demonstrator hurls a stone to riot police officers during clashes near Syntagma square during a 24-hour labour strike in Athens.

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© Reuters / John KolesidisSupporters of the Greek Communist party march to the parliament during a 24-hour labour strike in Athens.

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© APScreenshot from AP video.