ATHENS, Greece (AP) -- Groups of youths on the edge of a major anti-austerity protest in Athens threw rocks and firebombs at police outside Parliament, where the struggling government sought support for new cutbacks required to avoid a debt default.
At a rally of more than 20,000 in the Syntagma Square, police responded with tear gas to push the protesters away from barricades erected to protect the Parliament building and the lawmakers arriving to debate the new austerity plan.
Other demonstrators who had been part of the previously peaceful gathering also clashed with the violent groups of hooded youths, trying to eject them from their rally.
The protests were part of a 24-hour general strike against the new cutbacks, which the country must pass in order to continue receiving funding from a euro110 billion international bailout that is preventing it from defaulting on its debts.
A large part of central Athens was closed to all traffic and pedestrians as police mounted a huge security operation to allow lawmakers access to Parliament by car. Some 5,000 officers, including hundreds of riot and motorcycle police, used parked buses and crowd barriers to prevent protesters from encircling the building.
"Resign, resign," the crowd chanted outside Parliament. The protesters included both young and old, and many brought their children, hoisting them onto their shoulders to shield them from the crush.
Two separate marches organized by trade unions joined the rally in Syntagma. Such demonstrations have often turned violent in the past - three clerks died when rioters torched their bank in Athens last May.
But the latest austerity drive has brought many people onto the streets for the first time.
"What can we do? We have to fight, for our children and for us," said Dimitra Nteli, a nurse at a state hospital who was at the protest with her daughter. "After 25 years of work I earn 1,100 euros a month. Now that will drop to 900. How can we live on that?"
Her 26-year-old daughter, Christina, said the situation in Greece had led her to leave for the U.K. to study conflict resolution.
"I have no job here. There are no prospects," she said.
Police spokesman Athanassios Kokalakis said 10 protesters were briefly detained. About a hundred people booed and heckled as cars carrying Prime Minister George Papandreou and President Karolos Papoulias swept past for a meeting.
The general strike crippled public services across the country, leaving state hospitals running on emergency staff, disrupting port traffic and public transport, and forced radio and television news programs off the air during the morning. Journalists' unions called off their strike to cover developments in Athens.
Flights were also operating normally after the air traffic controllers' union dropped out of the strike.
"They keep asking us to give more," said Ilias Iliopoulos, general secretary of the civil servants' union ADEDY. "Now, again, they will cut our salaries and bonuses, from the little that we have left."
The government needs to pass a new 2012-2015 austerity program worth euro28 billion ($40.5 billion) this month - or face being cut off from the rescue loans from European countries and the International Monetary Fund.
To meet their commitments, Papandreou's Socialists' abandoned a pledge not to impose new taxes and have drawn up a four-year privatization program worth euro50 billion ($72 billion) - further fueling protests against austerity by public utility employees and other affected groups.
Some governing party lawmakers have publicly criticized the new cuts. One of them defected on Tuesday, reducing Papandreou's parliamentary majority to five in the 300-seat legislature. Another Socialist lawmaker said he will vote against the bill, which is set for final approval by early next month.
Papandreou faces an open revolt from his own party and a refusal by the main opposition conservatives to back the new austerity bills, despite EU pressure for cross-party support.
Papandreou met with the president to discuss how to solve the crisis.
"A national effort is required. Because we are at a historically crucial moment and a time of crucial decisions," Papandreou told Papoulias, adding that he was still in contact with opposition party leaders in an effort to garner cross-party support for the austerity drive.
"But on the other hand, everyone has to assume their responsibilities," Papandreou told the president, according to a transcript of their conversation released by the prime minister's office. "In any case, we will move forward with this sense of responsibility and the necessary decisions" to pull Greece out of the crisis.
The statements calmed concern, voiced mainly in the local media, that the prime minister might have been considering calling early elections.
The Socialists' popularity plummeted in recent weeks over the new austerity plan. A weekend opinion poll gave the main opposition conservatives a four-point lead over their Socialist rivals, the first time the party has been ahead in surveys since 2009. The next general election is scheduled for October 2013.
With its credit rating deep in junk status, Greece is being kept afloat by the EU and IMF bailout, but will need additional support to cover financing gaps next year as high interest rates will prevent it from tapping the bond market next year, contrary to what the original bailout agreement had predicted.
On Monday night, Standard & Poor's slashed Greece's rating from B to CCC, dropping it to the very bottom of the 131 states that have a sovereign debt rating. That suggests Greece's creditors are less likely to get their money back than those of Pakistan, Ecuador or Jamaica.
Nicholas Paphitis, Derek Gatopoulos, Petros Giannakouris and Lefteris Pitarakis in Athens contributed.