ATHENS, Greece (AP) -- Youths wearing ski masks hurled rocks and fire bombs at riot police as clashes broke out Wednesday in Athens during a mass rally against austerity measures, part of a general strike that crippled services and public transportation around the country.
Police fired tear gas and flash grenades at protesters, blanketing parts of the city center in choking smoke. Thousands of peaceful demonstrators ran to side streets to take cover. A police officer was attacked and his uniform caught fire in the city's main Syntagma Square, before he was rescued by colleagues. His motorcycle was burned.
At least five people were injured and another 20 detained. One group of rioting youths smashed paving stones in front of the central Bank of Greece, but there were no reports of any serious damage.
More than 30,000 protesters had attended the Athens rally, which had been calm before the clashes. Protesters chanting "Don't obey the rich -- Fight back!" marched to parliament as the city center was heavily policed. A brass band, tractors and cyclists joined the rally.
The rally was part of Greece's first major labor protest this year as Prime Minister George Papandreou's Socialist government faces international pressure to make more lasting cuts after the nation's debt-crippled economy was rescued from bankruptcy by the European Union and the International Monetary Fund.
The sporadic clashes lasted for more than three hours. About 500 protesters gathered outside parliament after the march and vowed to remain there until the government agreed to make concessions. Protest organizers at that gathering said they had been inspired by ongoing revolts in North Africa.
Prime Minister George Papandreou, on a visit to Finland, said he sympathized with the peaceful protesters.
"Economic situation (in Greece) is very difficult, and sometimes even I myself feel an urge to join the ranks of protesters," Papandreou was quoted as saying to Finnish national broadcaster YLE. "But mere protesting leads nowhere. We need decisions that can genuinely help fixing the problems."
The 24-hour strike halted trains, ferries and most public transport across the country, and led to the cancellation of more than 100 flights at Athens International Airport. The strike also closed the Acropolis and other major tourist sites.
State hospital doctors, ambulance drivers, pharmacists, lawyers and tax collectors joined school teachers, journalists and thousands of small businesses as more middle-class groups took part in the protest than have in the past. Athens' main shopping district was mostly empty, as many small business owners shuttered their stores.
Unions are angry at the ongoing austerity measures put in place by the Socialist government in exchange for a euro110 billion ($150 billion) bailout loan package from European countries and the IMF.
Greeks have endured months of pay cuts, sales-tax hikes and other drastic spending cuts, but protests have been revived by longer-term reforms including involuntary transfers for civil servants and new market rules to end protective job practices for truckers, lawyers, pharmacists and others.
Stathis Anestis, deputy leader of Greece's largest union, the GSEE, said workers should not be asked to make more sacrifices during a third straight year of recession.
"The measures forced on us by the agreement with our lenders are harsh and unfair. ... We are facing long-term austerity with high unemployment and destabilizing our social structure," Anestis told The Associated Press. "What is increasing is the level of anger and desperation ... If these harsh policies continue, so will we."
Elsewhere, about 15,000 people rallied and minor scuffles broke out in Greece's second largest city, Thessaloniki, while Anestis said around 60 demonstrations were being planned in cities and towns across Greece. He said the GSEE was in talks with European labor unions to try and coordinate future strikes with other EU countries.
Earlier this month, international debt monitors said Greece needed a "significant acceleration" of long-term reforms to avoid missing its economic targets. It also urged the Socialist government to embark on a euro50 billion ($68 billion) privatization program to pay for some of its mounting national debt that is set to exceed 150 percent of the GDP this year.
The IMF has said some of the frequent demonstrations against the Greek government's reforms were being carried out by groups angry at losing their "unfair advantages and privileges."